With the Dragonriding HUD many users might make their own vigor bar to match their WA for their characters. It would be nice to hide the combat Weakauraas while Dragonriding, and load my Vigor ones while riding. So they can share a screen location

Discovery notes:

• IsMounted() returns true while on a dragonriding mount, but that could have false positives for regular mounts.
• It's possible to detect whether a currently mounted mount is a dragonriding mount by running local mountId = C_MountJournal.GetMountFromSpell(spellId) where spellId is one of your currently active buffs followed by local isDragonRiding = select(6, C_MountJournal.GetMountInfoExtraByID(mountId)) == 4.
• There's also C_MountJournal.GetDisplayedMountInfo and C_MountJournal.GetMountInfoByID that return a 13th arg now that's "isForDragonriding", but both also take mountids and don't really care about current mount.
• A different option is C_MountJournal.GetCollectedDragonridingMounts() which returns a table of mountids that are dragonriding enabled that you own:
  
  Then you can run C_MountJournal.GetMountInfoByID(mountId) for each, where the 2nd return argument is their associated spellId which you can then check if it's currently active.

There is also a DMUI_DRAGONRIDING_SHOW event so we maybe could do that same as with vehicle ui

I didn't see that event DMUI_DRAGONRIDING_SHOW