Yeah, gimping it even more. Seeings as if you think about it putting your hand out while horse back riding is clearly the easiest of the three.

Lets not argue of the degrees
Of difficulty our characters experience casting
Spells as a
Justification for no magic (as of now) as that argument is boundless and terrible.
If i had to guess i would say magic will come
Later- things like cloak spells and master
Spells might be gumming up the works, because i think we all know people would try casting master spells while at full gallop.
Those issues probably Need to
Be addressed so it isnt all crashy when it is realeased.