It may be better, as others have said, for the Mark 1 version of the STG to limit itself to making small adjustments, rather than expecting it to change from say EADGBE to DADGAD or whatever. This would reduce the amount of power needed.

The firmware could be programmed to intelligently work out what the tuning should be, from the frequency of each string, and be preloaded with the most popular ones (EADGBE, DADGAD, DADGBE, etc.) or custom tunings that can be programmed in and downloaded via a USB PC connection. Then if it detects any difference in the actual frequency and what it should be, it could make the small adjustmants necessary.

This could be done on demand by the player, by pressing a button. Normally this could be done between tunes/songs, to avoid the player having to mess around on stage and annoying those members of the audience who hate paying to watch people tuning up.