That is an option for sure, but a very disappointing one. And it comes with a meaningful danger of ending up with 2 subscriptions: one yearly and one monthly. They really, really need to finish their “pay as you go” system. I don’t know why it’s not done yet and there’s been no word about it to my knowledge.
Maybe they should just enable a tip option? What do donations do to a company's tax liability and would it be worth their effort to enable something like that?