A few things to consider:

1. Battle system calculations have changed.

2. Spells can now be casted in pasive mode.

3. Featherfoot is like a refresh spell now so I think you can still recover mp while moving by using this skill.

4. Link and exp chain bonus system added. (being able to recover hp/mp while running might cause balance issues by allowing higher exp chains without much stategy)

5. Maximum hp/mp is getting increased.

So given how the entire battle system is changing it's probably a needed adjustment after it's been tested. The current hp/mp recovery is a left over from an old battle system that does not fit with the new system. I'm sure it will make sense once we try it out.