I mean, it's very easy to enforce. You just reject lists that are using Voltan units. It's so easy you could write a computer program to do it for you.
And they did effectively do that back in 6th and 7th. It was called the ITC ruleset. Which took a different approach to the problem, instead tackling the base rules to make a better game rather than the offending codexes. But the ITC is a really big deal considering it is effectively using fan rules instead of official GW rules.
Also this is one of the few times they could actually ban it and it not screw people over. No one actually has Voltan armies yet. Which is the big difference. This isn't 'your favorite army is finally good', this is 'this brand new thing no one has completely breaks the game.' And it's very easy to tell. And it isn't just math hammer. The rules are out and people are testing them via proxies and like. And Voltan are insane. And much like Iron Hands last edition, they are just as bad as predicated. Which would be a case where the prediction was 100% correct.