I believe the biggest concern with this in the past has been accurately accounting for load times during verification. It adds a lot of work for mods, especially the tighter the times get. There's no IGT or anything, so it either becomes honor system (not really a good idea) or frame-by-frame timing for mods (not really a good use of their time).
Ultimately, I'll let any of the mods chime in, but those are things we've mentioned in the past about it.
Yeah, that puts the verification process in the hands of the submitter more than usual, which can have some dangerous repercussions. While we normally submit our own times anyway, we don't usually make modifications to a timer plus those uncut times have to be cross-verified by mods. Making that process more complicated is (maybe) more than it's worth to them. Again, I don't want to speak for the mod team much more than this. Maybe they'd enjoy that sort of thing! But those would be my concerns if I had to verify.