UD Race Cavaliers are pretty much forced into using Dreadsteeds. While sure they're cool and can be thematic, I think it'd be nice if there were some degree of choice. Races such as Gloaming and Svirfneblin (I guess Duergar too, and Deep Imaskari if they count as UD race) are not races that are inherently hardlocked to the Underdark, they aren't 'Monstrous' races. I couldn't find any resource on the Dreadsteeds, but I mean, they're obviously 'undead' of sorts, which feels very focused towards Evil.
Here is the present situation taken from the Cavalier Wiki -
New mount available only for Cavaliers: Dreadsteed All UD Riders can only summon Dreadsteed as both standard and special mount. Exceptions are Drow and Evil Class UD Cavaliers can still summon Nightmares via special mount.
I propose that the 'Standard' mount option be set to the regular Cav variants, the Palfrey and such, so UD Race Cavaliers can pick between which to use. Alternatively, restrict this to Evil alignment, and allow Neutral to choose.