At this time we have a rogue external bot creating 10000 of accounts an hour, primarily at mediawikiwiki If we could see if we lower the throttle to one account per IP address to see if this reduces the impact. If there was a means to even turn off API creations for mediawikiwiki that would be helpful.
We have a temporary abusefilter in place that is inhibiting much account creation
though we are not able to write a really sweet filter for the usernames in use. We have edged back to a somewhat conservative filter that has a bit of leakage, though looks to be allowing the good accounts through.
I have a message about the abuse filter at https://meta.wikimedia.org/w/index.php?title=Stewards%27_noticeboard