I can't see anything at all going wrong with everyone setting off at 30 second intervals perfectly correctly and then working out correct riding times afterwards
. It's a nice idea though - just a shame Zwift don't make it easier for us to do things like that.
If we do all just set off together at least the lack of drafting (if everyone remembers to choose a TT bike - another thing it would be nice to make automatic when setting up the race) means it's still individual efforts being measured - and you can keep a close eye on those near you on GC - if you can keep up with them
.