On another forum, someone posted the THR22-100 partition table. I find it interesting TiVo spent the time and money to upgrade to the Premiere disk partitioning but not bring any of the TiVo specific features with it.
So even though the box acts like a HR10-250 with MPEG4, under the hood work was done to bring at least the base SW up to the Premiere baseline. Hopefully this shows at least a chance adding features in the future.
Also interesting is references to MRV in some of the log files. Maybe just dead code but just the reference of it shows the SW is "newer" then the last of the HR10 SW.