One letter Domains in danger of extinction

They are not in danger of extinction; there is almost assuredly someone willing to pay the 500 EUR price.

That person just isn't you.

Is it lame that nic.nu is doing this? Absolutely. Just pointing out they won't be extinct.

i own rt.fm and since it's a two-letter domain, it's now considered a "premiumplus" domain by the .fm company and would cost $5,000 just to register it again if i were to let it lapse. luckily the renewal is still "only" $100/year so i'm just kind of hanging onto it now.

if the $20 bought part ownership and a share of any future sale, then I think more people would be interested.

If you can't afford it, sell it :-)