I tell you what, I've flashed over 15 Xbox TSOP's via 007 AUF (I don't consider this a soft mod since you have to solder on the hardware to do it), and so far I see a 100% reliability rate. There are no issues with it at all.
A soft mod would include the font exploit, audio hack, or whatever else you'd use to load something like Phoenix bios loader etc. Flashing the TSOP is not a soft-hack. It has all of the same functionality that a mod chip has.
You could leave the TSOP writeable (after you solder a couple of points) and then flash the original bios back onto the TSOP when in your mod state, and then use 007 AUF and a hacked save to flash the mod bios of your choice back on. Just lock your HDD and then this would work like a software switch. On v1.0 and v1.1 Xbox's, you can wire a switch on the 1MB TSOP for multibank functionality etc too. Of course, you wouldn't do this if you were one of the people who thinks MS would tamper with your bios in the future if you left it writeable.
Like you said degull, if anything DOES go wrong during a flash, the box would be in very bad shape. Just put it on a UPS when flashing
