Welcome to the forums!
I think the idea has promise. I would remove the part about counting as a Province. It feels tacked on and only matters for a few specific cards (Explorer, Tournament, Fool's Gold, etc.). And maybe rename it (Battlefield? Wartorn Something-Else?).
I disagree with Awaclus on a few points. Yes, it's better when you can't trash your Estates, but I think that's fine. In games where you can trash your Estates, do you do so and buy some back later, or do you not trash them? Even in games where you can't trash your Estates, you might buy more Estates. So I think it might still be interesting.
I'm not sure further clarification is needed on the below-line part. You could add, "from your deck". But the rulebook is still going to cover common-sense stuff, like the fact that you trash those cards before counting up your score. ACTUALLY, you may want to change it to say, "Remove a Victory card from your deck" so as not to trigger Feodum's on-trash ability, which would probably cause confusion.
Cool card!