Its even more iffy due to quest progression and such.
IF they made any alliance change feature, the only way to avoid the worst of the trouble would be to limit it for after completing the whole of cadwells...

Which in fact would make a lot of sense too.
If done right.

I for one would love to see some special questline opening up after completion of cadwells gold, with an "loyalty called in question" theme, where your character gets to make a big decision...
- stay loyal to your alliance and find out who tarnished your reputation, spending the rest of the questline finding evidence of the frameup and hunting those responsible...
- or defect to another alliance, spending the rest of the questline courting your new home and preparing your escape...
Might take you all over your five "homeland" maps, and ending in either a big "prove your loyalty to your faction leadership" scene, or a daring escape a mere step away from your factions agents... come on, who wouldn't love to slam a porticullis shut in Razum-Dar's face while you hop on a boat bound for pact lands with Naryu, throwing a snarky one-liner back at your former comrade?

Of course... there ought to be consequences to becoming a known traitor. Perhaps a reduction in AP gains, as your new alliance isn't sure if they can fully trust you? This would also make such an option way less desirable for hardcore PvPers, who often are most wary of including such a feature as they fear it might unbalance the factions in cyrodil...