PLaystation is doing great but Sony isn't as good. Gaming could be split off.
XBox is opposite with MS doing great and gaming being meh. Could be sold off.
NIntendo is all over the place. Wii U was the second worst selling system in forever but switch looks ok.
MEanwhile Amazon, Steam, Apple, Samsung, etc. Could enter.
One leaving. I don't see a new company entering the console/handheld market any time soon.
Microsoft leaving however? I have no problem believing that, they are eroding the entire point of owning an Xbox anyway, at some point they might as well just get out. Nintendo should have gotten out some time ago imo, but their pride prevents them from it I think. Also I simply doubt that we'll still have consoles at all in like 15 years or so.
MS will probably leave consoles games focusing on PC with machine like Steamboxes.
Nintendo and Sony will probably leave consoles later focusing in portable/mobiles.
Nobody will enter.
The future is no consoles.
Sony, MS and Nintendo will be in gaming for a long time to come. Although I believe that all companies will keep a foot within the console side of things in some form, MS will move away from it more than the other 2.
So, I think a new console will try to enter before one leaves.