Coming back around to this, do we know what the changes to the Yellow paper will be to support this? When I went into it recently I found that even BEGINSUB would add more to the YP than I’d like. I’d be more sympathetic if this feature can be expressed succinctly there.
Also, one reason I don’t like this feature is that it prevents other means of implementing subroutines – e.g. I think Christian has shown that in some cases leaf routines can be implemented more efficiently with JUMP than JUMPSUB.