I had a Tandy 1000 TL/2; it had a tandy specific MS-DOS 3.3 with Deskmate setup in ROM, booted pretty darn fast; but you had to give that up if you wanted to boot a newer dos. A newer MS-DOS still booted quick, and there wasn't much to the BIOS before it hit the drives, but you couldn't run Deskmate on standard MS-DOS.
I realize at the time it wasn't very easy for most people but a computer that often receives upgrades via ROM is the Atari ST. I (sort of) recently upgraded my 1040. I bet one could produce DOS 6.22 replacement ROMs for the Tandy!
