To be honest, I'm completely satisfied with what PMBR has done. Regardless of whether or not the game is perfectly balanced, they've clearly made the game MORE balanced than Brawl while adding techniques, stages, characters and all kinds of stuff. 3.02 could be the final release and I'd be happy.
But the IDEAL 4.0 for me:
-Do the Ganondorf + Black Shadow moveset thing everyone's talking about. I REALLY want a new F-Zero rep, and this keeps the Ganon moveset (which I love, especially the thunder stomp) while adding more F-Zero. Other character slots could be filled or left empty, doesn't really matter, as long as if they do get filled then they're of the same quality as the rest of the roster.
-Some more/better costumes. Funny enough, I think Ganon could do with some better colors, since all of his are "dark with a hint of blue/red/green/whatever". It wouldn't be canon of course, but I'd like to see Ganon in gold armor or some other colors.
-swapping PS1 on the stage list with Distant Planet. Keeping PS1 as a counterpick is just a holdover from Melee where there were few viable stages anyway. It has two forms with walls that often just become stalls until it changes again, and the standard setup mimics PS2, so if you want to ban PS2 you should ban PS1 as well. I know this is more of a gripe with competitive rulesets, but I'd like to see PS1 phased out and in turn moved on the select screen.
-No new "competitive" stages. Going by Apex ruleset, there are like 14 already, maybe even 15? They all have different sizes, platform layouts, blast zones, and a few have walls to recover with. There's already a lot of variety, and the new stage Skyloft doesn't even really get played anyway. Making new competitive stages will slowly invalidate the banning process. I'm all for non-competitive stages, though! I miss Kongo Jungle N64 deeply.
-Reskin Dracula's Castle to be Bowser's Castle. Not sure why the devs added Castlevania representation where it wasn't needed, and I think Bowser's Castle makes a whole lot more sense.
-heavy rework of Jigglypuff's moveset - her current viability is centered around "remove options from other characters", and overall she isn't healthy for the game. I think Rest is a really big part of that, because it's a very weird anomaly that needs to be accounted for - if it gets too easy to hit Rest then it's too strong, but if you nerf the damage/knockback of it then it becomes useless. I think replacing Rest with Sing, giving her some recovery on Up-B, and removing a jump or 2 would be one place to start. Obviously not ONLY that, she'd need balance from there, but I think that's a start.
-Complete change of menus and announcer to be completely distinct from Brawl, incorporating more purple.
-TONS more Pokeball pokemon because pokeball-only matches are hilarious.
That's about it though.