With Game Stadia from Google launching this year,i think it will have a tough time atleast at the starting for 2 simple Reasons:

Always Online and No Offline Play

As it is a streaming service,you always need to be online.

Also,it is available on multiple platforms with different processing power and different architectures so games won't be playable off-line even if they wanted.

An Alternative is PlayStation Now which is playable online with streaming but certain games are also playable offline as the processing power is available on PS4.

The only solution to this would be standardization of Gaming Processing Power and Architecture like we have for Video.For example a Video is playable on any platform as long it is of a certain codec and Resolution.

For example a 4K MP4 video is playable on Modern Computers or TVs or Phones as it is standardized and it is cheap enough to emulate on most platforms.

For gaming an processing power is first of all not standardized and keeps improving.We need to get to level which is good enough.For example Intel Mainstream CPU processing power hasn't changed much for the last 5 years.

Software standardization can be done with software Tools and Emulation.

But there is also that Processing Power needed  for gaming is expensive and not like processing power needed for Video which is pretty cheap.

I think we will reach atleast some standardization of hardware in 10years time like Apple Shifting from Intel CPU's to ARM Chips on Mac Computers to standardization between Computers and Mobile Devices and that ARM Chips will have Good Enough processing power in 10 years to challenge Desktop CPU's needed for Gaming.

Also ARM Chips are cheap so we will in future see TV's,Tablets,Phones,Computers so all will have the same architecture come at a low price.

In future we will be able to download games on any TVs,Computers,Phones,Tablets and play offline like we now download and play video or songs

Games Library & Exclusives

It will have difficulty getting a good game library at first and with PlayStation Now and upcoming xCloud service which already will have a good game library,it will have a tough time competing.

It will also have a tough and long time before exclusives come to the platform.

It will struggle in its first years, but I believe that in a matter of years cloud gaming services like xcloud and stadia will grow in popularity naturaly with a much better tech + internet speeds always improve year after year.

Speculation: Google Stadia won't be as sucessful as some people think because the competition will probably offer something similar without sacrificing offline play. Sony and Microsoft know that It's too early to completely ditch Physical copies of games and there is many problems with streaming that need to be tackled in order for it to go mainstream.

I have no doubt it will be a slow start for Google, but I also think it will progress faster than some folks are thinking. As we move into the next generation people are going to start having to look at a device to play Call of Duty, Madden, Fifa, NBA 2K, Grand Theft Auto, and such. If Stadia has those industry leading titles, with Cross Play on PS5 and XB4, I believe a lot of casual players will just start using Stadia instead of investing in a $400 - 500 console.

For your casual gamer that only has a console to play Fifa every year, they can buy every new Fifa for the whole generation for the same price it would cost just to buy a next gen console. If they are using Stadia, not only will they get an improved game every year, but with ever improving server side hardware and internet, it will be like getting a new console and game every year. That is a pretty lucrative proposition for your majority audience. Not to mention it gives them access to the gam on every device they own, as opposed to one (unless PS Now and xCloud enter the mix).

My prediction is a soon the Internet connectivity get to point to the infinite fast and no lag , and cultural change and economic change happen across the globe, and many people prefer playing games on streaming. Sony and Microsoft already have a lot data center build around the world and still win by a lot of margin on gaming market share. Maybe 5 years won't be enough to invest, but two to three generation is plenty enough to invest in data center. Meanwhile for time being Sony will just focus on local gaming hardware and bit by bit build the foundation, the exclusive, build the market , build brand loyalty and build the infrastructure to the point where it will just streaming service.