After I updated a library used by the OpenID plugin, it seems that one can again log in through OpenID and also register new OpenIDs. Worked for me with the Mozilla Seamonkey browser; with Chromium I had to try twice, as the first time there was an error.
Let's keep an eye on this, and please report any problems. A pity that OpenID is not better supported in "the world's most popular open source forum".