Let me just play Devil's advocate here for a moment:
Supply bar filling? Really?
Where's the whole 'using your resources properly is a tactical decision' idea? Where's the min/maxing that you must do to even be remotely considered decent at games such as this?
I feel this is too simple, too forgiving a system. This sort of thing can be used tactically, sure, but it is also a tool for anyone who forgot to spend his resources properly and will not really get punished for it.
When your deck composition is not good you may find yourself with nothing to play on turn 1, or maybe a 2 cost card at turn 3, and so on. You need to make sure the deck has a nice resource-curve, and you need to use those resources properly or essentially 'lose' them if you don't. May I remind you that all of the abilities in the 'Trading Post' in play are ALREADY giving you options to act with spare resources (or sometimes, not so much spare, rather your need to draw a card or boost your future resources)?
I feel this is a bad idea, and if I sound harsh believe me - I'm a total noob when it comes to IW, but this feels too noob-friendly to me. We already have good mechanics to deal with spare resources, let's not make it any easier than it should be (and please - let's not make it an automatic, thoughtless, process that rewards you in the long run for being bad in the short run).