Book of 9 Swords? Works rather well I think for melee.
A good example. But these are still encounter powers. Just the dailies are missing.
I haven't used the Bo9S, but I've used the Warlock, which is a class that is entirely at-will based. He is a bit boring to play, to be honest, and adding encounter powers would make him more interesting. But there is one flaw I discovered that had nothing to with him being only at-will based, but with him lacking daily resources.
There was no way to be "decisive". If an encounter was a little harder (due to bad luck, or simply being a high EL), I really would have needed one of those Wizards 1d6/level damage spells, or even a save or die spell. I needed some "desperate" measure resource that I could use if I really got into trouble.
If the game system manages to avoid the bad-luck and more importantly the "very challenging" encounter part, you can probably avoid daily (or act/adventure/session) resources all-together. But you will curtail the variety in allowed encounters. There is less distinction between easy and hard encounters. And I think that was ultimately the reason why the 4E design team went for daily resources (in addition to the Healing Surges).
If you wanted, you could introduce a different meta-game resource, a "Action Point Deluxe" type resource (Drama Points? Hero Points? Possibilities?), that would not trigger daily powers, but instead allow you to use an encounter power again. (Maybe 2 such points per daily you would normally get).
There is still the "recharge" aspect of Bo9S powers. If you make it too easy to recharge, you run into the problem of people always repeating the same moves in the same combat, making it easier to abuse exploitable combos.
There are always trade-offs.