That's probably the best constructive criticism of VAR I've heard in a long time. I think they should do something like that - It would probably demand 3 times as many refs, to do each frame in the same amount of time though. Could this be done in other ways? I guess there needs to be a human being drawing on each frame, like in the current VAR?
The easiest would probably be to do a buffer-zone of 5-10cm, then also make that buffer-zone visible on VAR.
I agree with your general point that we need to eliminate these millimeter offsides, but with every "x cm leeway" suggestion there's going to be a discussion of whether it's actually x+1cm or x-1 cm, so it just moves the problem a couple of centimeters forward.
I really do think that a lot could be gained by using the frame before and after though as it's arbitrary which frame is used when they judge the offside.
I also think that a challenge system, where teams could challenge any call (while running the risk of losing a challenge), would be good.
That way, VAR doesn't have to check every decision and the onus is on the team that feels aggrieved to challenge the call. For example, the Wolves goal probably would've stood since nobody even considered that to be an offside worthy of challenging, which I think everyone considers a fair outcome, and Wolves could specifically challenge the van Dijk handball.
If they used challenges they could challenge any decision, and if the call is overturned then they get to keep the challenge. So for example we could've challenged the Williams "dive" and got Bardsley sent off instead by forcing a VAR check (or forcing the ref to go to the monitor and review, in which case it doesn't have to be clear and obvious since it's the main ref changing his mind on a situation that he sees again). Now the usual counter-argument to this is "won't teams use it to waste time?". Probably, yes, but they would be idiots to waste time by forcing a VAR check on an obvious throw in because that check would take three seconds, and they'd be idiots to waste their challenges on those calls if the other team ends up scoring a handball goal in the 93rd minute that is missed by the referees.