While I agree with you in principle, the quick answer here is boring and simple - we want to attract contributors, and people have GitHub accounts. Someone made an Issue about this early on and multiple external contributors were against it, so it’d pretty clearly be bad for momentum.

normally zdoom stuff has backwards compatibility so this is a real edge case because lilith makes bugs happen on purpose - and those bugs have been fixed!

with 3. you might be referring to a GitHub discussion I commented on
to be clear, lilith does a check to make sure its running on zdoom 2.8.1 since the mod only works on that
if we somehow made it “playable” it wouldn’t work like its intended to - and we’d be disrespecting its own check anyway

decorate will stay deprecated, as zscript is - at its core - decorate with the rough edges removed so that new features could be added

it basically is that for GZDoom, but AFAIK the Z in ZDoom is just that the creator chose the letter arbitrarily

Doom has always had proper Z axis support since 1993 - certain routines in the game just ignore it, presumably for performance