First off, I want to say thanks for putting out these ideas. They provide a variety of suggestions and ideas on things people could consider writing or getting a dev to produce for them. I have included some responses/notes to several of these. In some cases, they're are about how you'd go about making setting this up, for others it's further expansion of the ideas presented and for some its pointing out issues or possible things to be wary of.
Group of goblins
These would be best handled as a modification to the existing creature (similar to how the male/female version of several creatures work). This sub-variation should not show up until the player's 3 levels lower than the combined mob level (unless playing in hard mode). Since the goblins come in both genders, these mobs should probably be a mix of males and females. Player victory would provide the player the choice of grabbing one of their choice of gender to be their victim, the rest escaping - in this way, the same scenes could be reused (though maybe a few new options could be among them as well). Player loss would probably have the player mob-fucked, though players blocking guy or girl content would have the unwanted gender watching and waiting while the others 'have their fun'.
giant feral rat M LVl5-7
This is a good idea and suits the area.
jackal M LVL8
The jackal infections are special ones for Nermine's quests. Being able to get one outside of this kind of undermines the specialness of that.
reptilian watchman M LvL8-10
It is worth noting that this is quite similar to the existing Wolverine Guard.
cockroach M LVL5
I'm guessing you suggested this guy because of the 'hotel' thing. Not 100% sure how I feel about this thing, as it breaks the 'equine' theme, but does go with the hotel one to help make up for that. The horses probably wouldn't like having them around and would probably be trying to get rid of them when spotted... but given how hard it is to kill a normal cockroach, a nanite-healing roach-guy would probably recover from even the worst hoof-stomping.
rider F LVL5
This is a very good idea, though I'd dial it back to them being more human-like, only having horse tails and maybe ears. This'd help make them more different from the others. But that'd come down to whatever the writer chose to make them in the end.
Stables: Some domesticated "ferals" would be nifty
As random encounters are found while wandering the halls of the hotel, this would mean those feral horses would be in those halls as well. While you could make some excuse about the player wandering outside among the paddocks, that'd keep showing up every time one of these encounters occurs, quickly straining credibility. Suddenly the player's outside after searching inside, especially after doing an event that's clearly somewhere inside the 'hotel'. I'm not saying they're out, but it's cumbersome and would take some clever writing to work around this sort of thing.
Feral dogs in the city
While a good idea in general, the Outside area already has 6 canine forms: 5 dogs and 1 wolf. And that's after I shuffled several of them around.
Angry cows and bulls in the plains
Don't you mean... 'Mad Cows'? *eye-roll*
Feral Lions would be a cool addition to the park or the zoo.
The Felinoids are quite similar to this suggestion already.
Oraganised groups
See my notes above about the Goblins. The Hulking Cheerleaders aren't a good candidate for mobs, both because they're a strong foe individually (lvl 9) and because they are in a sex competition with each other.
Degenerate soldiers
This is an interesting idea, though the general impression we're given about the military immunity boosters is that they're temporary, so soldiers who degenerate in this way probably quickly forget to use them and are soon transformed by their wild search for sex. Another option would be to make them more like the Corrupted Spawners and have a random assortment of infected traits to show their waning immunity.
Hulking Nurses:
Not sure how I feel about this mash-up of the Vixen Nurses and the Jaguar Orderlies. Might make for a viable new sub-variation for later into the Hospital Quest, should that content continue. On the whole though, some new creature/staff member would be better for expanding the area.
The Bukkake Mass
While an interesting idea, the Sealed area (under Trevor Labs) is considered sealed for both story and content reasons. This allows the more disturbing/horrifying material down there to remain separate so players not interested in it don't have to deal with it. Letting this cum girl amalgam out (and past Orthas and her fire breath) breaks both of these. Also, given how the Cum Girl grows and grows based on player semen/femmecum absorption before finally splitting into two to reproduce, having some of them come back together to form this monster goes against that progression.