UPDATE Nov. 15th: This evening, I watched the recorded livestream of today’s Second Life Town Hall with Grumpity, Oz, and Patch Linden, and I wanted to add an update to this blogpost about the eagerly-anticipated ability to change your SL user name.
Grumpity reports that the team at Linden Lab is still working on it, but this project has been more complicated than anticipated. She now estimates that this will be released within the second quarter of next year (2019), rather than this year, which is definitely a major disappointment.
As for the cost of this new service, Grumpity estimates that it will be “on the order of a few months of Premium membership” (which is currently US$9.50 monthly, or US$22.50 quarterly, or US$72.00 annually). So expect this to cost about 20 to 25 dollars, which is about what I expected.
Grumpity stressed that these name changes are not meant to be (or replace) display names. She added that it should be possible for you to go back to a name you had before (for a fee).
Linden Lab will also be accepting suggestions from SL users for possible new last names, so watch for that announcement sometime in the future!