Okay, so, yes: I installed 10041 yesterday from Windows 8.1. Went to the Windows Insider page to kick off the install, which actually started with 9926. After a few rounds up (somewhat funky) updates, was given 10041 as an update and I successfully installed it. After yet another round of updates, I'm now in the process of downloading 10041 AGAIN, which frustratingly is going very, very slowly.
I'm very curious to see what happens when the download is complete. I'm guessing I'll get an error that it can't be installed, which will likely stick with me through this build as the phantom system update stuck with me through 9926.
Honestly, I have no idea why I'm putting myself through this process. I keep turning a perfectly happy and functional SP3 into a bloody nightmare. I need to have my head examined, I think.