However: There already exist a lot of stock photography online stores out there, and they work quite well.
As for graphics templates and stuff (Illustrator, InDesign), I'm not so sure... Graphics professionals probably won't need them, anyway. And whether consumers are ready to shell out money for templates...
Your last question: Photoshop is dominant as in a monopoly. I don't think this will either make Photoshop sales rise or decline. But I _do_ find the situation poor. There was a time when xRes (was that Macromedia?) had a little chance of taking some customers off Photoshop. But the application (PS) just has been refined over the past 15 years to a degree others can't seem to match. And while there's still a lot of things one could want have added to Photoshop, I think competition will have a very hard way to get anywhere near its level. Also: They would have to have the same things but better - and for less money. And while PS is surely an expensive application, it's still relatively cheap for what you get.
But back on topic: I'd quite surely try out an Adobe Stock Photography Store. But we (the company I work for) already have good sources for stock photography.