A Luigi wishlist thread?
I don't think all of this would be justified lol. He'd be really broken then.
More run speed + bigger upB hitbox = upB would be too good of a punish
Especially if you give dtilt 3 less endframes so dtilt trip to upB would probably be a true (kill-)combo.
Now what I'd like to see would be useless or really bad moves made somewhat usable,
DownB not that hard to mash for without momentum,
and just a little better movement.
So...
Utilt could get a small buff. It's only rarely useful, because of worse range than usmash, and generally you'd rather go for grabs anyway. Maybe make the FAF 1 less instead of your suggested 2, or else it could end up like Fox' utilt maybe, which would be way too good. Maybe the hitbox should stay out longer above him to make it easier to catch someone in it (somewhat like Marios utilt). Something like that.
Dtilt: really, really bad move. It definitely needs something. Less FAF seems like a good idea since it feels really bad and even if you hit with it you don't really gain anything from it. But I guess the opponent shouldn't be able to trip from it so you don't get a free upB after. Maybe just a little more knockback. Make it hit like 20° or something, Idk.
Maybe dtilt won't be able to trip at upB KO-% with more KB like you suggested so that could work as well.
Ftilt: give it something.. anything that makes it useful. 98 % of the time I rather jab. Ftilt really needs some kind of use to make it more useful... maybe a little bit less startup, a little more range. Just a bit.
Dashattack: give it more range and burst momentum (think of Smash64), maybe not a multihit as well, or make the hits connect properly. Almost every dashattack I do is a misclick. So it'd even help me if he didn't have the move at all, even if it can have a use very seldom. Also a bit less endlag so you don't eat a smashattack if it's shielded/dodged or you miss.
SideB: give it higher priority/a bigger disjoint, just a little bit. It's pretty useless and only for recovery, where Luigi gets a big sign with the text "please gimp me" on it, since it's soo laggy. It should probably get a few frames less endlag, though I'm not sure if that would make it too good of a recovery move. With just ~2 frames less endlag it shouldn't be too big of a deal, though.
DownB: easier to mash (make it able to buffer inputs like in Brawl so you're able to mash normally).
Airspeed: a bit better would be really nice.
Luigi feels like a slow brick in the air that can't move horizontally. SideB is too laggy to be useful as a recovery or get-out-of-juggles-tool. It really misses the whole point of it existing.
DownB is way too hard to mash for realistically. Even the best mashers mess up, and if you have to do it too often you won't be able to do it anymore since you'll be too exhausted. That's not how it should be.
All his tilts are almost useless since his usmash and jabs are better tools by far in almost every situation.
His dashattack is more of a hindrance than it helps. It's so laggy that it can always be punished really hard if you don't hit with it or even if it's just shielded, and the opponent can easily fall out as well to make him able to punish it.
A little more airspeed would really help him a lot. Makes him not needing to never use his doublejump onstage or else if he gets hit offstage without it he's almost as good as dead.
It would also help him to make crossups in the air since right now it's easy to punish any landing aerial. For Mario it's a very viable thing to do to keep your opponent guessing on which side you land.
Another thing I could see is giving him more KB on his fair. It would stop combos from being too powerful sometimes and make it more like it was in Melee. If he can threaten with a strong move in front of him it would also stop opponents from trying to combat it since their reward for hitting through or trading is much more than their risk of getting hit right now.
The most helpful would probably just be airspeed, sideB less endlag or easier downB. His recovery is so easily punishable and he's moving so slowly that he never wants to be in the situation. If any of these things would be changed it would make it a bit less terrifying for Luigi.