As time passes new technology that makes bigger limits for consoles, PC, & Phones come and go, but all of these all compete for the same market and pull things off in ways that make them unique.
At some point something may give and the first competitors that may give up the ghost are consoles. These are the medians that hit the most mainstream audiences when it comes to game platforms. They don’t have the power of a PC nor do they have the limitations that mobile games have.
However we had a long-lasting generation in Xbox 360, PS3 & Nintendo Wii that stayed longer then most console life cycles. Usually consoles last for at the most 5 years there some exceptions like the NES which lasted until 1995 as well as the Gameboy but it’s still quite rare for consoles to last that long. This generation took advantage of leaps and bounds that made games for their time look amazing and lot of games for the Xbox One, PS4 got ported to the predecessors because they could handle it.
Now we run into the problem of consoles trying to act like PCs but end up coming off short because their not PCs. The other point is that handhelds won’t be lasting very long either the 3DS at some point will have to leave, the fact the a mainstay Pokemon title for the Nintendo Switch to me, is a sure sign of the 3DS near the end of its life. Mobile platforms are picking up the pace in its place.
The question now is when will Consoles become obsolete. The honest answer to me is when development for consoles becomes as expensive as a PC. Building a PC can be expensive ($500+ is usually what the cost is).
This question is also vital because Sony’s big success currently is in the console market because every other business is outclassed or shut down. The day consoles become obsolete will a problem for Sony, Microsoft has many other ventures they can pursue and Nintendo still knows how to develop games themselves.
Finally how long will it take until console development becomes as expensive as a PC? My honest prediction would be 1-2 generations of consoles and after that it may pointless to develop consoles. It will take time but the Mobile Phones have the potential to take the place of consoles along with the additions of augmented reality & virtual reality.