Maintenance for the week of November 4:
• [COMPLETE] ESO Store and Account System for maintenance – November 6, 9:00AM EST (14:00 UTC) - 6:00PM EST (23:00 UTC)
Mounts placed in your homestead should be rideable.
If you place a mount in your own home and maybe even send it on a route, then you and your guests should also be able to ride them. That would only be logical in the context of the Home Tour Update.