I'm guessing that the reason this sort of construct is not directly supported in "non-blead" perl is that, as a syntactic form, it has an inherent sort of ambiguity about it

No, it was a blatant bug that made it not work (along with other things such as qw/1 2/ * 3). I'm pretty sure the recent fix will be included in 5.8.8 in due time.