Well competitive mode is right around the corner, it's meant to be released by the end of the month (although they're cutting it a bit fine, and not clear if that included consoles, but it is out on Public Test Realms).
Competitive mode is more than just ranked play with seasons, there's another factor where you're expected to treat playing both sides of a game (attack and defense on escort/assault maps) as two parts of the same game (whereas in quick play people often quit after one), and if the teams draw over these two rounds there's an extra sudden-death mode. Control (King of the Hill or what drahkon called capture and hold) is also best of five rather than three.
Also I definitely think they will bring other modes and maps down the line, they must've covered development costs now with sales and loot boxes, Overwatch is doing very well. Blizzard has a history of strong post-release content updates. I imagine they will add a lot more skins and make some of them super rare to tap into that hoarder market even further.