Instead of Vayne's Ult giving AD, give it more utility?

If it comes with nerfs to her ability to solo lane that sounds interesting. That would make her even more safe as a top laner than she already is, which is something I really wouldn't wish on anyone playing a more traditional top lane champ.

Going invisible and gaining more MS when chasing isnt enough utility now?

That wouldn't be great for a few reasons. First and foremost, she is an ADC and he primary role should be damage not CC. Second, they would need to buff her damage elsewhere, which would then make her too oppressive in laning as she wouldn't have as well defined a window of power. And third, a longer knockback would be pretty bad for her due to her short range. The only way such a long range knockup would help her is making her way too good at setting up ganks, which is a toxic playstyle imo.

yea I want vayne to push me into other galaxies

I once posted like...2 years ago Vayne lacks what makes it fun for being a "van helsing" or "demon hunter". Van helsing, Dante from DMC, Bayonetta. They all have these large arsenals in their disposal. Vayne pretty much lacks the visual point appeal compared to them.

So I posted how about adding additional effects to ALL her skills on her ult and nerfing stealth. And at that time it got a bucketload of upvotes. Like condemn adding a explosive. Adding a one time usable active W skill like Riven.

How to save make a champ a stun bot in one simple step

I wouldn't mind that. Or maybe increasing her tumble distance and upping the movespeed bonus. Make it a real risk/reward scenario instead of all reward with the AD spike.