This just pushes him further into support. You have more opportunities to proc passive when not farming and facing two people, and more roam potential. Converting more and more of your damage is effectively just giving him mpen for free, also supports weren't really especially building mpen over mids already. The Q change actually makes support insanely stronger, and would probably even motivate more mpen purchasing. It's not that difficult to switch to hitting split Q's over direct when the incentive to do so is this extreme. Also the stacking passive has the strange effect of reducing the incentives for full combos, if I'm already doing 100% true damage to someone why does my ulti passive matter?

But these changes are just all very over the top numbers wise and would make Vel the strongest hero in the game no contest.