To solve the fighter issue, we would first need to determine exactly what they were trying to 'fix' by watering it down. Assuming they didn't want a constantly-marking
scorching burst, I think the following idea would work. That is, make the restriction, "You can't use this feature with at-will powers from your non-fighter class."
That would allow you to mark with encounter and daily wizard powers, for example, but not constantly run around marking with
scorching burst and
thunderwave. If that still proved problematic, then just cut the whole other class . . . but do it exclusively, so that the fighter/X could still mark with basic attacks and
dragon breath.
Also, deadsmurf's idea from several posts ago was pretty much what I was going to suggest. My version's a bit different, so here it goes: tag the 'striker' class features with some kind of keyword, like some of the features are currently tagged [hybrid]. Then say that only one [striker] feature can be used per round. Under this method, the avenger's oath could also be tagged [striker], so as to be mutually exclusive with hunter's quarry, etc. For things like the barbarian's
howling strike, the power could be specifically keyed in the barbarian hybrid section as counting as a [striker] feature, so as not to function with warlock's curse, etc.
Keterys stated he thought deadsmurf's version of the idea was broken, but I'm not sure why. I don't think it excludes striker/striker combinations from being viable, in that having two different [striker] features just makes you more versatile in applying your damage (or whatever). I guess warlock/ranger would be kind of silly . . . but that's true for many reasons

Sneak attack/warlock's curse would be great; curse when you don't have combat advantage, and otherwise do sneak attack. Even if you had CA all the time, cursing could still be useful for some powers/effects. Also think of a barbarian/avenger, who would
howling strike when charging, but otherwise roll twice when his oath would apply. These combinations are more versatile in their striker-ness, just as a defender/defender has more versatile (but not stacking) marking.
This method also solves the problem Asmor brought up a few pages ago (which is also something I had considered before reading this whole thread -_- ), which is the prospect of some future supplement introducing cross-class powers. That is, a power that is available to both rogues and rangers, and is therefore accessible to both classes, and is therefore benefited by the [striker] feature of each, according to the current hybrid rules. I guess this is kind of weird design space that may never actually develop, but the fact that at least two people have considered it means it's something to watch out for.
An alternative would be a derivation of my above fighter suggestion . . . just specifically exclude the 'other class' from gaining benefits of your [striker] feature. This way you could still apply one or the other to your basic attacks and whatnot. Then the issue is if you multiclass into a third class and can apply both [striker] features to powers of that class since it isn't either of your 'other classes' . . .
Another thing . . . my version of the pdf shows the warlord gaining a second use of his
word at level 16, but not the cleric. Is this intentional? Perhaps to prevent a warlord/cleric from having four
words at level 16? Perhaps because the cleric's Healer's Lore is considered to be powerful enough to make up for it? Or maybe it's just an oversight one way or the other . . . thoughts?
Anyway, I'm really excited about these rules overall, and it's something I've wanted from the multiclass system since before 4E came out, so I'm really pretty excited . . . plus I'm excited about some possible designs it opens up for writing third-party products . . .
As a final note to everyone who's said they were making hybrid versions of PH2 classes: none of you has stated what you did with the druid's beast-form/non-beast-form at-wills. What were your solutions? You can't just make the druid choose one or the other. Maybe one of each?
~ fissionessence