Role DIversity

Starting off just straight to the point. Will we every see a competitive team comp in the future that does not include a marksman?

This isn't a thread complain that marksman are OP or anything. I'm asking a straight forward question. Riot always promotes Role/champion diversity and no matter how you look at it marksmen are the only constant. Each of the other roles can play a smaller part or successfully be substituted with another role. This is because it's not the role that's is important, but what they are doing. Tanks for example are about defense/bulk and crowd control, but both those things can be provided from a source other than a tank. CC can come from mages/supports and bulk can be provided with bruisers. Sustain damage however seems to always fall back to marksman.

This brings up alot of question: What off sustained mages like Swain, why aren't they viable for this role? What off non-ranged carries like Yi, could they ever fill these shoes? Is this actually an issue?

Is there something I'm missing? If there is, I humbly and respectfully ask to be enlightened.