I'm in the process of updating previous Z2 characters. The goal is to have everybody up-to-date to release Gohan as we update everybody, and have something consistent.
That being said, this means I'll probably ask several questions to them combo pros, in order to ensure I understood their feedback correctly. 
I removed the ability to jump cancel if the opponent has blocked Sliding Kick.
However, what you're saying is I should completely remove the ability to jump cancel out of Sliding Kick even if the opponent was hit by it (in order to avoid the empty cancel bug), but in exchange make it special cancellable (even if P2 has blocked sliding kick ?) into :
- Ki Blast (qcf+P)
- Machine Gun Temper (qcb+P)
- Wolverine Flip forward/backward (qcf/qcb+K)
Did I get this right ?
And for the 2nd part, you're saying to put "air.fall=0" instead of =1 to all Ki Blast moves, which will hopefully not create other weird stuff later on ?
This is a good idea, but this actually hurts Vegeta's cool rush-pressure style quite a bit; which in light of the way other characters work (SSJGoku's teleports and warp kamehameha threat, Goku's bicycle kick threat), he only really seems to have qcb+fireballs in the air for any kind of truly unique rushdown (wolverine flip is reminiscent of the other chars' strings in some ways) once dash HK's cancelability on block is gone. This is a fine change, but personally, I would miss it.
Underlined:
Spoiler, click to toggle visibilty
First, let's consider that if dash HK is not cancelable at all anymore, or is only cancelable on hit, the followup from qcb+P is made much, much less worth using, as you'll get punished to hell for trying this to get in. This is one of Vegeta's only other ways to get in on his opponents however, which is what he wants to do; otherwise, he's just using instant airdashes + normals, which aren't exactly unpredictable in any way.
Jump canceling dash HK at all really isn't a necessary addition as the only -realistic- thing this allows you to do, without considering the insane pressure he gets with it that does not need to exist in this manner (and his current empty cancel) mind you (so that we're thinking about this realistically and practically), is to either combo into his air normals, such as j.HK, loop with it using air down-back-forward+P super (has to be done in the air to be able to be looped), or cause a hard knockdown, which is what dash HK does right now.
That's really not that much, when the empty cancel is gone.
Now, if you were to only make it special cancelable, what he -can- retain is the essence of his old crazy pressure using it, while giving it limits. Right now, counters are extremely strong, they completely take away certain options on block as -very rarely- are they able to be blocked (ex. the CPU blocking my counter as I countered his jab). Knowing this, any attempted "blockstring loops", such as dash HK into qcb+P and repeat will not work when they have bar. You'll get punished with a counter, leading to a knockdown, which is not where you want to be in a fighting game.
In other cases, such as with qcf/qcb+K, he has a great way to keep the pressure on you without making it completely insane, as dash HK into qcf/qcb+K has very easy to see holes. Wolverine Flip can be contested if he doesn't do the followups, and Wolverine Sweep (as well as Elbow) can be blocked. Both Wolverine Sweep and Elbow aren't cancelable, so he can't do a ton off of it if it does hit you. Dashing back after Wolverine Flip, or dashing back and using the Elbow, or just doing nothing after the dash. These are all a TON of options that he has, while all having holes and parts where they can be punished, especially if the opponent has bar for a counter. None of them are as crazy as his empty cancel/jump cancel mixups, yet he retains their essence this way.
As for fireballs, yes, that would be optimal, since I don't believe fireballs need to knock down...like at all. They already work so well as combo tools on the ground for SSJ Goku and Vegeta, Goku doesn't have a ton of use for them, but that's because it's his style. But with this, any "fireball juggle loops" will no longer work, or at least they shouldn't work I'd hope. It may need some fine tuning if not. But definitely take away knockdown fireballs.
And I'm in no way a hivemind on this stuff, but I like to help out. Don't take what I'm saying as the "professional" way to go about it; this is just from my experience and knowledge on FGs in general. Vegeta is my favorite out of the demo three, because he's fast and his game is to pressure you over and over and not let you breathe, while Goku and SSJ Goku are all about threats and scaring you out of pressing buttons (or INTO pressing them), so this is how I would see him turning out if you wanted to fix him up.
And again, the only problem you're facing after all of this is done is the possibility that qcb+P into dash HK and repeat may still be an infinite juggle even without fireballs knocking down. Dash HK after qcb+P DOES take some time to activate though, so it just depends on how things go.
Hell, if you wanted to, you could just...only make it cancelable into Wolverine Flip. That'd be the end all fix right there, if you were to go along with the special cancelable idea. Then you'd be good, since Wolverine Flip is itself jump cancelable, and you retain all that pressure stuff I was talking about. Bam. You're set. No possible loops (there is one with dash HK into flip but it's only 3 times) or infinites at all.
I might've posted too much. Lol. Y'all can punch me for it later.
