Wall o' text incoming!

I know Short Spine Syndrome has been knocked back before, but I'd like to bring it up for a re-visit as we have a lot more mutations both in-game and upcoming now that would be fairly harsh IRL!

I'll go over three of the most common reasons against Short Spine Syndrome fairly quick, but if you have more reasons please put them in the thread!

Firstly: Short Spine Syndrome would render a lion unable to survive in the wild.

I don't think this is quite true- we have quite a bit of evidence now that shows that wild animals with Short Spine Syndrome can survive in the wild.

There are the well known cases of adult, or near adult animals that have been shot by hunters (An adult wolf shot in Russia, Adult fox with the syndrome, sub-adult coyote.)

There is also a short video of An alive adult Raccoon with Short Spine Syndrome that is seemingly doing pretty well for itself!

In addition, we have mutations in-game that render a lion unable to hunt (Blind, Eyeless, Deaf-upcoming, Clawless-upcoming) but due to the fact that lions work in a pride, they are fed regardless. We also have mutations that greatly hinder hunting (Dwarfism, Achromia) and an upcoming mutation (Toothless) that requires pride mates to tear up bite-sized chunks of food for their pride mate.
So impacted hunting ability wouldn't kill a lion with SSS.

Secondly: Short Spine Syndrome would result in early death due to internal deformities.

While we can't say anything for the wild animals that were shot, there don't seem to be any serious internal organ deformities associated with SSS- two dogs with SSS, Pig and Cuda, both had x-rays that showed that their organs weren't actually impacted all that much by their deformity. A lot of the 'shortness' seems to come from their tails and necks! So death as they age wouldn't be a necessity.
I can't say anything about their ability to breed, however- for obvious reasons, none of the dogs with SSS have been bred (neither has the horse), and finding any offspring the wild animals may have had would be impossible .

Thirdly: All the cases are in dogs, not lions!

As seen above, while most cases have been seen in dogs cases have also been recorded in foxes, coyotes and raccoons. A case has also been found in horses, and while it's not a feline it shows that SSS is not restricted just to canines.
As SSS is so incredibly rare, it could very well just be that a case hasn't been documented in felines yet.

So from this, I think we should definitely not count Short Spine Syndrome out instantly!

It could be a mutation that is visible from birth, and that causes a penalty to stats- maybe half of what a cub should have had. SSS lionesses could be able to hunt, but would be much more ineffective. SSS lionesses could be broodmothers though!
Not sure on Kinging. While I lean towards allowing them to be kinged (as Dwarf lions can be kinged, and they are also pretty handicapped on the whole hunting/fighting side of things), I'd love to see some other arguments!
On patrolling as submales- same as hunting lionesses. They can do it, but will be much less effective.
On reproducing- honestly, I can't find anything regarding SSS and reproduction. While I doubt males would be impacted, I honestly have no solid opinion on SSS lionesses reproducing. While an SSS lionesses internal organs wouldn't be impacted, pregnancy is another matter; I'll leave that open for anyone else to decide on

Tl;dr: Short Spine Syndrome itself would not kill a lion, has been found in multiple species, and any reduced hunting ability would be made up for with pride mates sharing food.