I dunno... I think as a player I am kinda beyond "mains" now. I'm a causal, no doubt. I really like playing but I am not a "top of the ladder" kinda guys or going to be attending any high level competitive events... it is just all about fun for me nowadays. Maybe 2 decades ago it was like that.. but now... I basically play most of the roster over the course of the life of the game.
I suppose out of the officially revealed stuff the ones that I'll probably try first are legacy ones. Sub-Zero, Radian, Lou Kang etc etc... as you can jump right into them but I also played a TON of SunGod in MKx.. so I think Kotal Khan will be my 1st deep dive. In fact in MKx I was really into D'Vorah and Khan so seeing them both back is hyper fucking awesome.
To be honest I think this is looking like one hell of a roster. Apart from some that I consider ,duds like Noob and Erron Black, I can see myself playing all of them. No Sindel is a huge blow though : (
I'm a contrarian though. What ever are the most common characters I see in the online modes will be the ones I do not play and w/e is the most uncommon is likely to be the ones I play the most.
Also I will be playing in w/e mode allows move customisation .