This could be a spirited debate! In many cases, you are correct that many folks do not use their DSLR's to their full capabilities. With the current and future improvements in technology, the average person does not need a DSLR. The professional, on the other hand, still needs the flexibility and capabilities of the DSLR. Going forward for the professional, it will be the end user (magazine and newspaper editors, clients, etc.) who will determine the quality and what they will be satisfied with. An example is the Chicago Sun-Times newspaper who laid off their entire photography staff, which included several Pulitzer Prize award winners. For every day reporting they rely on their reporters with a cell phone! I would like to hear Danielle's (Photo Chick) take on this because I think she does studio work. What is the future of cameras in the Studio? In sports photography, the mirrorless options (for the majority of cases) haven't advanced far enough to be useful. That doesn't mean that in certain situations they couldn't be used, just that the extra expense of a $700 camera for that limited use, doesn't make economic sense for the pro. Interesting future to say the least.
Agreed that it's not there yet. But it is quickly moving in that direction.
For a sports shooting pro --- Let's remember, that this is a $650 camera, compared to the $5000+ cameras that pros often use. So can't expect it to match the $5000 pro camera in all regards. But the fact that we are even having this conversation, is pretty telling.
If Sony's claims are correct (a big if), it can focus as fast as those big expensive pro cameras, and it can shoot bursts as fast with full auto focus (11 fps). What is unclear, is whether you have full control over Aperture and shutter speed during those fast bursts. More likely, the aperture needs to be wide open in order to get continuous auto focus. Another issue, compared to the pro cameras, is that the EVF often lags the action when shooting fast bursts. So certainly, this $650 camera is not a total replacement for a $5,000 camera being used for a sports professional.
Additionally, in terms of native lenses, there is less lens availability for the system then for other systems. Though this is likely to change over time.
Still, aside from the professional sports photographers, this would seem to handle "action" as well as most other cameras on the market, if not better. (Another open question is the depth of the buffer, which has plagued some Sony cameras. 11fps sounds nice, but if the buffer is only deep enough for 1/2 second burst..)
From what I have seen, mirrorless cameras work very nicely in the studio environment, where focus peaking and similar features really allow locking down focus with perfection. As a brand, the downside of Sony in the studio, is that it's wireless flash system is not as good as Nikon and Canon. But that's not a dig against mirrorless, just against Sony.
Myself --- I'm rooting AGAINST this technology because I'm invested in Sony A-mount, which may become extinct, lol. But if I try to be objective, I personally prefer a dSLR-type body. I don't mind a little extra size to better balance the camera. I like in-body-image-stabilization as I have very shaky hands. I like having more direct access to controls with more buttons and control wheels. And I like that there tend to be better lenses, at better prices, available for traditional dSLR mounts.
But I fear that in the long term -- sleek and compact tends to win out over traditional and tactile.
There were many who doubted iPhone would ever become a major success because it was thought that large parts of the market would insist on physical keyboards. But over time, the people who did insist on physical keyboards saw their choices dwindle in the smart phone market.
I suspect, in the next couple of years, you will see Canon and Nikon introduce new lines of mirrorless cameras that retain their traditional lens mounts. They won't "start over" as Sony has.
