I would not miss the ability to mount or dismount during the battle - historically not many cavalry did that with the kind of ease that a human player would do so in TW if given a chance.

However, I can't see there being much of a technical computing problem with mounting or dismounting before battle, MTW style, even with the RTW engine. Just swap one unit card for another. Having the ability to do so would greatly enhance the historical accuracy.

Personally, I'd like to see foot knights have more of an impact in M2TW than they did in MTW, although I agree they should not be recruitable (and so we need the ability to dismount them).