I think more backgrounds/guilds should have riding available to them. I know
that this could be a min/maxer problem for combat, but why not make it so if
you have 0% combat riding you get the message:

Fight whilst mounted? Are you insane?
Your mount bucks you and runs away. (-50hp)

I mean if any tiger can steer a ship, then I think that most people should be
able to ride a tame mount with appropriate mount gear. Obviously some
limitations would be appropriate (must have combat riding for
chimera\'s/drakes/water beasts/etc...).

I think that an elder nun should have the ability to ride a goat, or a female
druid on a unicorn. Or an evil priest riding a black panther.

At the moment there are so many of the wonderful outworld beasts that are just
not worth taming. How about a Sprite riding a stoat!

At one point I talked to an arch about this, and they didn't seem too opposed
to perhaps having squires guild available to all backgrounds...I'd personally
like to see, though, a few other guilds have lesser mount stuff added. Like
templars might get some basic combat riding, etc (maybe max templar gives
access to cavalier guild?)
One other option is to add some basic riding skills to explorers
guild...enough to ride a horse. The "mount balks" suggested above wouldnt be
necessary because without combat riding skills, you'd get thrown from mount
right away anyways.