[2023] Monthly subscription fee to get BR locked?

AFAIK we do not have any plans for such option. MM is same for all players, no matter if you support game development with money or you are 100% F2P player.

If you want to suggest something, please use Suggestion Section here: https://forum.warthunder.com/index.php?/forum/572-moderated-suggestions/

If you want to discuss MM, please use this topic: