"Radon" or "Radium": a one-time purchase that is lighter than Plutonium

I doubt this could really work as a monthly subscription. After VAT and Stripe fees, I'd estimate Fluxer only keeps around ~€3.5 for every €5 subscription payment, even less so in countries with higher VAT like Hungary. A cheaper subscription, like a €2.5/month one, would be hit even harder, probably around €1.5 per purchase. You could take a page out of Migadu's book and have it be yearly-only for the lowest tier, so it could be €10-20 a year, maybe? Either way, though, I definitely wouldn't add a subscription entirely focused on discriminators. Federation v2 will almost certainly affect usernames and discriminators, and considering it's relatively high up on the roadmap, making a subscription, much less a one-time purchase, based on a feature that might not exist in 2 years would be a waste of development time and consumer money. If discriminators still exist after federation v2 is added, then I think this could be something to be considered. Until then, it's hard to justify.