You could probably write a book about Sony's camera adventures or the digital photo revolution. I just look back 10-15 years or so and see a period where an activity that was always quite popular attempted to become a mainstream product. There have always been photo enthusiasts, it just took off to a point where few would have believed it - camera makers went ga ga overloading the market with tons of compacts, super zooms, DSLR's lots of models. Then bang it all went south...financial crisis hit it as did the phone cameras. The enthusiast market never went away nor will it, but the mass market did. Most people who bought into cameras/gear in a serious way were always there when digital came along it was a big fat cow to milk.
Some say it's the phone cameras partly but not entirely true most people who "bought" a camera back in ye film days got a compact or semi enthusiasts a bridge or SLR. Compact users rarely upgraded there wasn't any point unless you lost the camera or broke it. That part of the market was never sustainable for digital because these users just don't keep buying cameras never did even in film days. Phone cameras got better to a point where many people would skip on replacing or buying a camera so that killed off that old turkey almost - there will still be a market for them just nowhere near the size it used to be.
IMO Sony had a very good chance back in 2006 but they didn't really get what people were looking for so they played around with different ideas hoping something would stick. Maybe E mount will for me the lenses are horribly priced I suspect a good share of their buyers are using Canikon glass on their bodies. For A mount I'd expect a drip of occasional releases maybe the A77III later this year the A99II surprised some..A68 will be around for a bit can't see that getting replaced. A99 is still sold fairly cheap for a FF body so maybe they will keep it going for a bit. I see no point moving mounts.
The open nature of E mount is appealing..that's it's biggest downfall long term you're no longer locked into buying a single lens mount. Can't say the prices on E mount lenses are good compared to the big 2 so it's a non starter for a native system. E mount is a sensor in a body that's the appeal to many. Sony will probably run with 3 bodies for SLT all the makers are struggling Ricoh are losing money on Pentax evidently and Canikon are having problems. Glory days are over..what they are trying to do is get more profits from less sales by targeting the higher end market and price increases or premium stuff. Just like the RX series they're looking for £1000 odd for the latest MkV really a grand for a 1" sensor compact? Fair enough if they get people to buy it