Sony has rolled out the A9, the A7RIII and the A7III fairly recently. That represents a fair amount of up front money in a stable to shrinking market. I wonder where they are in terms of their sales targets and whether they are in a frame of mind to roll the dice again.
I think Sony definitely see a way to stay ahead of the curve by always having a camera in waiting to trump whatever it is that Canon and Nikon announce.
Now, given that Canikon release cycle is 4-5 years in the FF market, will Sony keep releasing at this rate? I doubt it. Firstly as you say is the money. But also, as I have said elsewhere, the cost-benefit curve will fall off quite rapidly.
40MP to 60MP? Who cares?
In-camera focus bracketing - nice...but how many will actually use it?
17 stops DR vs 15 stops? Who cares beyond a few pros? You only need to go onto Instagram and Flickr to see what the mass market think of blown out highlights and blocked shadows (hint: they don't care)
Yes, the enthusiasts will keep most manufacturers happy to a point, but in 4-5 years all brands will be pretty much on a level again and you will be left (again) with 'which name do I know' - and that will be CaNikon with Sony a meritable 3rd.
However, Sony have a habit of producing high tech stuff that is way ahead of whatever it is that the customer needs and then dropping out of it quite quickly when the customers do not prove to be as hungry for it as they first thought: Vaio laptops for example or Betamax as a lesser example. Both had distinct advantages when you looked at the drivers in isolation. The Vaio fitted the laptop brief perfectly for a portable system but to get something truly useful you had to bolt on all sorts of bits and pieces which people found a pain in the butt (that old interface/useability thing again being a far second to the technological capability).
Similarly with their camera gear, people like sharp images, and the Sony cameras fit that fantastically well. But as the fading camera market shows, the number of photographers for whom sharpness is a key driver is minimal, and as with Vaio haptics will play a part and I think Sony, like Olympus and Panasonic will move into larger bodies when people realise using a small form camera handheld all day can be uncomfortable. And once they do that they will move back into Canon territory.
And there is also the emotional side - newbies still want 'cameras like the pros use' and by the time the idea that that means DSLRs is dispelled, there is a good chance that CaNikon will be firmly entrenched in the mirrorless market and useability will beat technology in the deciding factors.
And (as with Vaio) will that 'meritable 3rd' be enough to keep them in the market? Their history makes me wonder.