The following is mainly for @matsan, but maybe it helps someone else too.

If you want to renew your Apple iPhone Developer Subscription currently, the checkout process is borked, if you use the "intended" way (clicking through). I did find out a way, how it does work nevertheless (hopefully). I didn't get the confirmation mail with the activation code yet, so maybe this was all wrong. But I got a confirmation mail, that I ordered it :)

I did btw inform Apple approx. 2 weeks ago, but didn't hear anything of them.

Update: It actually worked. I got the activation code 25 hours later.