As a slowish player, I beg you not to enforce timed games on everybody (unless the time limit is pretty generous).
I understand those people that want their plays to move along fast, but playing fast extremely reduces my enjoyment of Dominion. Adding a preference for the time limit (fast vs slow) in a way similar to how vp counters work now would keep everybody happy, I guess, but at the cost of slower matchups.
As a player that likes to take his time to make a play I am interested what you consider slowish?
There are some morons that start insulting you, if you take 10 seconds to look at the board and other people that take forever for some reason.
Imho a player should time out a lot faster, if he does not perform any action whatsoever and is clearly not present. I am perfectly fine with people taking their time, but some people are clearly doing something else, besides playing the game. In fact in a particular slow game I decided to start cooking and coming back every 5 or even more minutes was not a problem at all, which really should not be possible.
As it is you can very much make the other player resign, if you so desire. I did this to a player, which starting insulting me after the mentioned 10 seconds. If you want to you can take a really really long time for each of your turns without timing out.