I considered putting time in to customize Mephisto, or to move forward to edge Mephisto, or to switch to one of the other Rails systems like Type or SimpleLog. But ultimately, I came to the conclusion that tweaking blog software isn't really something I want to spend time on. There are good, mature, open-source systems available, so I might as well run one of them and get on with the rest of my life and business.
The change is not, alas, completely painless. WordPress does not understand how to import from Mephisto, so I hacked together a bridge for the past content via RSS. But I didn't move tags or comments (and I doubt I will ever find the time to do so). And the URLs for individual articles have changed (bad blogger, no biscuit). But moving forward, I hope, things should be stable.