most NFEs are strictly outclassed but Doublade adds a solid check to Terrakion within the metagame, while other NFEs like Porygon2 and Type: Null (a worse Silvally but can slow U-Turn) could potentially have useWhich are the pokemon that can be useful with this update?
Gonna use this post to make another point I saw someone ask in the OM room: The purpose of this unban was not to introduce new viable Pokémon into the meta (though it will be nice to see if Doublade will hold up). The reasoning behind the council's decision was that this ban has been in place since Mix and Mega's infancy, but there were no reasons to continue restricting 50% of Pokémon from mega evolving. While Chazm did disagree because he believes that it doesn't follow the rules of mega evolution, but the rest of the council was in agreement that either A) This isn't exactly relevant as almost everything in Mix and Mega doesn't follow the rules of mega evolution or that B) this change is so small that it doesn't cause any problems.
TL;DR This unban is most likely going to be insignificant on the meta and was only put in place to have less restriction on the tier, don't look too deep into it