It will have his niche player base, but it won't explode or be anything close to CoD popularity or anything. I say that because after extensively playing Overwatch and also trying out the game pad control scheme (no, not in a real match, I'm fully aware of the controls discrepancy between mouse and game pad) I feel like this kind of game doesn't translate well with joysticks. Why do I say that? Well console shooters uses lots of subtle tricks and design decision to accommodate the control scheme and make it feel as natural as possible.
Design tricks in most console fps:
- The base movement speed of players is fairly low.
- The action is mainly in the horizontal axis (few reasons to shoot up or down, even Blops3 reigned that down following AW which did not have that design).
- Most console shooters favor hitscan, or if not at least very fast projectiles.
- Bullet magnetism and aim stickyness makes aiming pretty pain free.
- Most shooters on consoles feature aim down sight, which is often coupled with a target snapping, making it easier to engage mid/long firefights with having to be super precise with the stick.
- Turning around with a joystick is often awkward and slow, so map design and sprint lets you disengage instead of fighting back if flanked.
Almost none of those design tricks are present in Overwatch, making it feel like a PC shooter shipped down to consoles. Characters move much faster than your typical console shooter, and some are particularly hard to hit like a good Genji. There's barely a horizontal line for action. You have to look up past your maximum vertical field of view at the default view angle for Mercies/Pharahs, high perched Snipers or people on rooftops while your can't go there (say your Tjorbiorn vs a Junkrat). You also have to 180 turn from time to time, like against dashing/recalling Tracers or Genji dashing through you, which is awkward with sticks. All of the above makes it much more frustrating to be efficient at both aiming and looking around.
Regarding aim assist mechanics like aim stickiness, it's there but with slow projectiles characters like Lucio or Mercy that mechanic is a trap. You have to actively move out of the stickyness zone if you ever hope to hit someone that is ADADing, else you will never hit them because you have to actively lead and predict, but now you have to fine tune your aiming with a joystick out of the sticky zone. It feels really awkward. The game also lacks ADS which isn't a big problem since very few heroes are designed for mid-range fighting but it does make McCree and S:76 harder to play with at those ranges.
All of those above makes me think that while the game will be a huge success at launch on consoles, the huge population won't stay and people will go back to what they are comfortable, feeling like they have trouble getting kills and playing good in that game without really knowing why. I predict it will have around BF4 level of population past the initial hype, which isn't shabby.
I like this write up, and hopefully they have taken this all into account. Blizzard isn't afraid to change how a console port plays vs the PC version. See diablo 3 and the roll mechanic, along with other things. I expect to see some of these things, minus the zooming and snapping which will be a loss for a console game. If it is a straight port with just minimal adjustments then everything you say could very well be true.