Yes, it would. I don't see why liches can't be different, though. As you point out, lichform isn't a clear-cut advantage -- you get most of the drawbacks of mummyhood in lichform, and by the time you could cast a dual-school L9 spell, you probably don't care too very much about your better aptitudes or hungerless casting. Despite the flavor-awesomeness to the proposal, with more thought, I am left wondering when I'd ever choose this route. Crawl is not an RPG
One other thought: if the supply of phylacteries is severely limited (1-2? per game max), you could potentially break yours to return to the living -- a very limited desperate way to let you quaff !curing if you're confused, or maybe something you'd do when going for the dark rune. Or if you really, really needed revivification.
One other other thought: perhaps, when making the lichform transformation, you're given a special opportunity to transfer your now-useless transmutation skill, at a severe penalty (25%?), to another skill. Ash could remove the penalty altogether for this one-time transfer.
If combined with the 'break phylactery to return to life' thing, it gives an interesting choice: do I keep my tmut skill in case I want to return to lichform later or go back to blade hands-ing things after Tomb, or pour my tmut skill into something immediately useful -- maybe I can get Fire Storm online with that experience... but good luck leveling tmut enough to return to lichform in that case.
I am not a very good player. My mouth is a foul pit of LIES. KNOW THIS.