@bucky: That's okay if firestall lives. Immorush is a bigger problem, IMO, and the immolation/deflagration nerfs help there.
@kamietsu: That's a cool idea about having the mark modify your quanta cap. I don't think 50 will be a very significant quanta cap for most decks, though, so maybe a slightly different effect based on mark might be better. I like the idea about the mark changing things up a bit that way.
@atico: I suppose stoneskin isn't too bad at healing 50hp. It's just that most of the time, it's going to heal much less, which is why it's balanced; if you want a really big hp gain, you have to keep it around as a dead card for a very long time first.
@mormegil: Pretty much agree with all that, though I think RoL/Hope might suffer somewhat from the 50 quanta cap, as it won't be able to build up quanta for fractaling dragons/archangels as easily. I never played this deck much, after finding out it didn't make electrum as fast as my other decks, so I'm not sure if the 50 quanta cap will make a big difference on that deck or not.
The only decks that will be hurt significantly by the 50 quanta cap are those that rely on stockpiling a VERY large amount of quanta. If you can get up to the 50 quanta cap, you probably have a lot of pillars/pends already out, and you won't be able to spend it fast enough. Decks based on Fire/Ice Bolts/Lances, Drain/Siphon Life, Stoneskin, Fractal, and Dissipation Shield/Field are about the only ones I can think of that will be weakened in any significant way by this, and even there, it will be mostly in PvE; in PvP, 50 quanta is a lot rarer.