Sadly, it's _far_ more powerful since it lets you stack striker damage or multiple defender types or any of a number of other things.
So modify it thusly:
Focused Initiate
Requirement: Level 11+, any multiclass feat that grants an at-will attack power as an encounter attack power.
Benefit: Choose an encounter attack power that you gained from a multiclass initiate feat. You can use that power as an at-will attack power.
If you don't mind me asking, exactly how many choices are there for such a feat? I don't recall any multiclasses off the top of my head (though I have little knowledge of anything beyond the PHB) that grant you an encounter attack power.
Unless, of course, you mean allowing someone to turn another class's encounters into at-wills (via power swap feats). That would be WAY too powerful, since encounters are typically encounters for a reason.
Yeah there's also the Druid and Invoker multiclass feats.Off the top of my head, that would be the wizard and warlock multiclass feats, but there are probably a few more.
My curent character is doing paragon multi and actually as a half elf, with the Versatile Master, he gets to choose an enounter, utility, and daily from ANY class list.
This feat gives much less than Paragono Multi and could supplement PM because you would be able to have 2/3 first class, 1/3 second class (or 3/4, 1/4 for human) at wills.
DC
The issue isn't that it's too powerful, IMO. It's that it only benefits a tiny handful of multiclass feats and leaves all those who grant limited class feature access out in the cold. If you're trying to design a feat to boost multiclassing effectiveness, you should try to come up with something that will help any multiclass character, not just the three or four that actually grant an at-will attack as an encounter power.