I hope, we agree on !in and !is, as the current lexing introduces the shown parsing problems. But !is needs to be added to the IsExpression rules then.
Hmm what if you have something like Templ!is(T:int)
Is http://d.puremagic.com/issues/show_bug.cgi?id=5785 fixable with grammar changes other that !is being one token? I haven't had a look yet how UFCS is expressed and how it could affect this.