My personal feelings:
If a setup is closed (What is included in the game is unknown):
It needs to adhere to a setup closer to that of an accepted Mafia Wiki "Normal" setup. The players should not be left feeling like they have no idea what to expect. "Anything" should not be out there. There's still room for the mods to play around with just how many PR's are in the setup (PR heavy does NOT = RMM), but the types of roles that can appear should be within a reasonable standard. I look to setups like C9++ (the most common "normal" setup run) as a great example of what "normal" roles to expect would be. Certainly this can be expanded SOME, but not heavily. If I'm in a closed setup and cannot have a basis for expectations at night, or how to explain things, then I feel like I'm in an RMM game.
If a setup is open (What is included in the game is known):
I think a "Normal" setup here can get a lot more leeway. Here mods can have fun and explore unique mechanics and still call the game "Normal". Because at the end of the day, as a player, I can come up with reasonable explanations for any set of events. Maybe the whole setup here isn't spelled out. Maybe just what COULD be in the setup is (see C9++ for a great example). But as a player, I know what to look for inside the game, and this makes my ability to PLAY the game, especially in a straight scumhunting manor (something I think "Normal" should strive for) much more functional. Had Modern Community fallen under this category, I wouldn't have any problem with it being called "Normal". The same goes for Robz' games in the past, or any of the others that have been run that push the limits. This is actually why I find Cayvie's games (while not always BALANCED) to absolutely be of a "Normal" variety of game. Everything that COULD be in the game was pre-stated.
Anything falling into the above two categories to me is a fine and "Normal" game. Both categories can push PR heavy, or PR light, to whatever degree the mods feel like doing. They can be flavor heavy, or flavor light, and they can be a lot of fun. The key to both is that the players should never feel shocked or surprised. They should come into the game knowing what to expect. If that's a closed setup with more standard roles, great. If it's an open setup that could have crazy shenanigans, that's fine as well. What crosses over into RMM territory for me is when a setup is closed (what's in the game is not known), and the mods push the boundaries of Role creation.
Basically, to paint things in a very broad brush:
Normal Games with a Closed Setup may contain:
Cop
Doctor
Roleblocker
Vigilante
Godfather
Rolecop
SK
IC
Mason
Neighbors
Neighborizer
Tracker
Watcher
JoAT (with listed roles above)
Modifiers:
1-shot
x-shot
Bulletproof
Godfather (in the case of, say, a SK)
Maybe a few other standard roles/modifiers that I've forgotten. But a fairly tight format. What's possible is within reasonable expectaions, even if the number of each is unknown (PR heavy // PR light). I do think a normal setup should strive to contain at least a HANDFUL of VT's or Goons. Especially in a closed setup.
Normal Games with a Semi-Open / Open Setup may contain:
Anything short of alignment switches or cults. I tend to disagree with the community here in that I dislike busdrivers or janitors here (I feel they start to stretch the imagination on what's possible within the game a bit too far), I wouldn't throw a fit to see them included, as long as it was stated that they are possible within the setup. The basic goal here isn't to state exactly what's included, but at the very least what may be included.
RMM games to me should almost always be Closed Setup, unless the mod really wants it open for some reason. I think alignment switches and cults are both acceptable here, as long as they don't go overboard. I think RMM games should still STRIVE to be balanced, but that shouldn't get in the way of the Mods having fun with their creation. PINL is ALWAYS a rule in RMM games.
Inventing / Tinkering: If you are planning on running a closed setup, and wish to label it "Normal", I do not think any Inventing / Tinkering should be done. This goes back to the players knowing what to expect. If I come out and claim "Investigator", I think the reasonable expectation in a closed setup is "Cop". If it turns out I'm a gunsmith (I investigate for clues to see who might have guns), then I feel like the mods have put something in to mislead reasonable expectation. If this were an Open/Semi-Open setup however, maybe Cop/Investigator/Tracker/Whatever are all possibilities. At least I know ahead of time that there's a difference between Cop/Investigator. Further, if you're going to modify a role that already exists on the Mafia Wiki, I think the modification needs to be spelled out ahead of time (even in an Open/Semi-Open setup) - because you, as a mod, know for a fact that players will refer to the Wiki when they see that Role. And reasonable expectation is that the role does what it says.
Essentially, this all comes back to "Reasonable Expectation". As a player in a game rated "Normal", I don't want to be put in a situation where I have to solve the mod. I don't want to feel like I've got no idea what could possibly be out there. I don't want to feel like I need to account for "everything". If I'm unable to get the most basic of handles on a game, then I feel it's no longer "Normal", because I can't play as if it is.
Lastly, on the point of "Reasonable Expectation", I think this is where Voltgloss got upset in Modern Community. He felt that, if you include a role like "Ninja", there's a "Reasonable Expectation" that there's a Watcher/Tracker. That's a fence that I sit on both sides of, but it's not an issue to me that makes or breaks "Normal" vs "RMM". I've no issue with a setup that contains a Godfather, but no Cop. So I shouldn't have a problem with a setup that contains a Ninja with no Tracker. I shouldn't have a problem with a setup that contains a Strongman, but no Doctor/Bulletproof. Yet I DO feel like all three examples LEAD the players to believe the existence of A means B. Which I think brings me back to the two setups of "Normal" that I think should exist: If you're playing a closed setup, the mods should strive to avoid any misleading. If A exists, then B probably should. However, if you're running an Open or Semi-Open (C9++) setup, I think it's perfectly reasonable for one to exist without the other - because it's prestated ahead of time that this could be the case. There's no expectation upon seeing Ninja, or Godfather, or Strongman, that there MUST be a counter-role in the game.
Lastly Lastly: BM:
First off, I don't like the PINL rule that we have. I think mods in ANY game, of ANY format, should adhere to this. The BM games where this is not the case I have found systematically fail to be fun for the players. Players need at least SOME structure. And that structure needs to come from the mods. BM games to me are games that have completely wacky GAME mechanics. There should be no expectations on the roles, and the game may play in very weird ways. This is why mods must always remain truthful. Because you actually get MORE creative room when you are. Let BM games be anything they want to be, but be honest with the players at all times, and you can really have fun with them. BM games generally don't try to be Mafia games. They follow a Mafia format of Day/Night with lynches, but beyond that, my expectations here are "Have no reasonable expectations".