Well, getting third party support for a new console might be pretty difficult for one thing. Yes, it might use the same processor as an existing machine, but the games would still have to be ported over, and you'd also probably need a decent number of unique games for the platform too. As a result, you've either got to convince third parties to invest in making games specifically for an untested system on the assumption it'll catch on later, or go the Nintendo/Microsoft/Sony/Valve in house route and make the games yourself, which is a whole 'nother kettle of fish. So getting the necessary games/support is a challenge in of itself, even if your hardware is on par with existing console manufacturers.
Then there's the whole challenge involved in actually marketing the thing. Why would customers buy this? How much would it cost to advertise a brand new system in an era where the major console manufacturers are spelling millions (probably billions) on advertising and have about a hundred times more name recognition than you probably will?
As for cloud gaming... that's proven to be quite the technical challenge in of itself, and even companies on the level of Microsoft and Google are struggling to get it to work flawlessly right now (or to sell the public on the idea in general).