A self-deleted post is often not a low-quality post and may simply be a mistake noticed by the user, unlike moderator- or community-deleted posts which may indicate serious problems that the user may not recognize or may have intentionally posted. Should they carry less weight in the question ban algorithm?
Self-deletes already don't matter, provided they are self-deleted after at least 30 days.
We have -- or should I say had -- many, many abusive users who felt they needed to:
ask, then delete and ask again so their question would go to the top of the pile and get answered more rapidly.
remove 'evidence' of asking many low quality questions. What low quality questions? I don't see any!
Largely a non issue at this point, unless you have specific examples.