@Asper, I'm wondering why you're so against the while-in-play clause. I like it because it's something simple, new and unique that has some really interesting implications. I particularly like what it does to Pearl Diver, Wishing Well and Ironmonger. You said you've tried something like it before; did you find problems with it in testing?
I tried a card that uses the bottom of your deck to store stuff for later. Diving Bell instead uses the top of your deck to store stuff for later, by making you draw from the bottom instead. There isn't that big of a similarity other than that. As i said, your idea works much better, and the reason i dislike the "while in play" thing is mostly that it alters how another card plays. Considerations like "Which card takes precedence now?" aside, it feels a bit unelegant. I don't know about any better way to do it, though.
What cards do you feel are problematic? I don't think it's any harder to figure out than Trader replacing gains, even though Trader is optional and this is mandatory. This just replaces draw with draw-from-bottom.
I didn't think they were problematic, just not pretty. And Trader is already causing us Blue Dogs. In general it does the same weirdness the -1 Card token does, like ignoring Farming Village. Which is okay if there's no other way or the concept is just too good to not do it because of this, but it's still a negative thing. Thinking of which, can i lose my -1 Card token and still draw from the bottom of my deck? As far as i know not. But i can choose.
Another thing is that the card tells me to draw cards. It's already in play, so i guess i should draw from the bottom... But, why does it stand below there, i already drew these 2, what to do now? The timing is obvious to experienced fan card analyzers like us, but it's confusing when compared to official cards. A similar issue is why i made my "Minister" (which gains according to cost and reduces cost) not "while in play". Of course, using a "this turn" wording isn't really a better option for Diving Bell.