There's something on Reddit that has some rumor post going on. I'll re-type what it's saying:
"Raiden's the main antagonist. Base roster planned to be around 30 characters with 10 as DLC. Plot borrows elements from Deception and Armageddon. Characters that I've seen lots of artwork and rendering include Kano, Li Mei, Noob Saibot, Nitara, Bo Rai' Cho, Johnny Cage, Shang Tsung, Jade, Taven, Daegon, Cassie Cage, Jacqui Briggs, Frost, Kenshi, Kotal Kahn, Jax, and Onaga.
Characters that died in MKX are not coming back for 11. NPCs in story mode are returning. Story mode will again be chapter base but longer than any previous ones. They're bringing back variations and brutalities too. Game should be out by Spring 2019.
That
is all I know at the moment.
Hope that helps, bro.
Now get off my dick about it."
MKX's ending makes me believe that the main antagonists will either be: Liu Kang, Kitana, both or someone else (e.g. Shang Shung, Onaga, Shao Kahn, someone new). I just think that Raiden will pretty much be what he said in the end, someone that shows no mercy to enemies but still fight for the good side. Would that create conflict with the rest of the good guys? Sure it could, but I don't see him as the main antagonist.
Other than that, there was a lot of negative fan feedback for the whole too many human cops and their kids too roster so I don't see them putting three Cages again plus Jax AND Jacqui (Sonya is not listed but yeah). As far as the others go, it seems like a totally fake roster considering how conservative they've been in MKX with 3D era characters. This dude claims we'll get Li Mei, Nitara, Bo Rai' Cho, Taven, Daegon, Frost and Onaga. Onaga could be a possibility, but all the others? MKX only had Kenshi, Shinnok and Quan Chi, an NRS favourite (and fan favourite of course) and two boss-type characters. Bo Rai' Cho and Tanya as DLC and they didn't even give us Fujin after a ton of demand for him. Considering all the above, I sure as hell don't see the base roster having Li Mei, Nitara, Taven, Daegon and Frost.
Last but not least, I am 100% sure we will not have variations in the next MK game, it will be replaced by something new, perhaps Injustice's Gear system + something else or just something else brand new.
Conclusion for me: Fake rumors