Maybe that could work, then again not sure if setting a full limit is good.Works well for rated games of chess. If every competitive game follows the ELO system because its perfect, why not use their time system which is fair?
I would argue that chess is fundamentally different. The strategy in chess is more intense and involves thinking many moves ahead, thus a timer become necessary for competitive chess. It allows you to spend minutes on a single turn if you choose to, but you're sacrificing your overall time clock. IW is very strategic, but not in the same way. There's only so much you can consider during any one turn, hence it's appropriate to limit each turn but not to limit the overall match (I think). Plus, notice that you're suggesting a rule set that's even stricter than in chess, which is that you want to keep the individual turn limits and add a chess-type clock on top of that.
However, if you're going to bring up chess, I'll refer to a system that I personally prefer much more, which is go. In go, you have an overall clock, say 30 minutes. But once that runs out, you have a separate set of very small increments that you revert to. (These are called byo-yomi, for anyone familiar.) For example, you may have 5 sets of 30-seconds each. You only use up a byo-yomi period by exceeding your 30 seconds, at which point you move into the next one, until you have none left. If your turn lasts less than 30 seconds, then you keep that byo-yomi period. I prefer this much more to a hard time limit because you don't automatically lose if you took too long earlier in the game, however you are penalized because in a game of go, 30 seconds isn't much time and you're forced to think faster and risk making mistakes in the end-game.
I don't bring up the go system because I think we should use it. As I said, I think a game like IW is fundamentally different and doesn't need this at all. I just wanted to point out an alternative, more flexible system with plenty of tradition and proof that it works.