This perhaps explains the reluctance to allow unfettered looping. On initial inspection, R3Alpha eventually returns TRUE for parse "" [while ]—it may be the unbreakable nature of Parse loops were already mitigated(?).
 is a match on any input. And I'd like some  to be an infinite loop.
I mention in my linked post that sometimes decaying to infinite loops is a feature...and here it certainly can be. Consider some [:(...)]. It may be that on one iteration it evaluates to null and hence vaporizes. But on the next pass it might evaluate to a rule which splices.
(Curiously, there's a difference between some [:(...)] and some :(...), because the first evaluates the group on each pass while the second evaluates just once. To understand why, see "When should parse rules notice changes?")