It's not impossible. Every offside incident differs but we know what the offside rule is. You're either offside or you're onside. If there were clear rules around handballs in the box either attacking or defending then there would be consistency. You'll always get the odd one that is marginal or very hard to decipher and so there will always be a talking point, but that's fine. The system would work efficiently and enable the majority of decisions to be correct.
In cricket the Umpire's Call rule is controversial. The umpire didn't give it out but the ball is shown to be clipping the stumps, it's not out. Surely that's the umpire getting it wrong then no? But the system has a margin of error and as the ball didn't actually hit the stumps, a computer programme tracking the ball is suggesting it will, then you have to accept it.
If the rules were clear and the the FA developed scenarios, even with supporting examples with images - wouldn't take too long to do, then it would speed up the way VAR works.
A lot of the issues people have aren't with VAR, they're with the rules themselves. We don't like the handball rule, and it needs resolving. But that's not for VAR to do.