We've added in some things that weren't originally in Brawl, and I think some fresh ideas that further set us apart (BRAWL REPLACEMNT! lol) could be in good taste if done right. All changes don't have to be a buff per se, but if you argue for why we should buff luigi, why was Fox given JC Shine? He didn't need a buff imo.
It varies the gameplay, makes him a more unique character, and unlike some stupid PSA hacks out there ppl make, I actually think this could be pulled off nicely
As for values it's all just estimations, doesn't have to be 5 secs. Yea thats too long lol. Maybe like 3? It opens up some neat edgeguarding options for Luigi. Even though the player would see you're about to go high and they might recover low, it's all about options. You could also go high and sort of follow them down waiting to punish an air dodge.
It's also unlike the gdorf utilt which this is adding in new content not modifying it. And the gdorf utilt was canceleing an extremely powerful move whenever you wanted, when this would be stopping a... jump. Not like a crazy strong attack.
I don't think this should just be thrown into Bp, but I think it would be interesting to see at least and to give it a shot in testing. No need to be added in the rush for RC1 though, unless it was made in like a day lol