I think the possibilities created by something like Rasberry Pi in conjunction with Linux will be the only alternatives available if you don't want to buy into somebody's walled garden not too long from now.
But once that happens, the next step will be to get Linux and FOSS outlawed by locking down ALL hardware.
The easiest way to do that would be by requiring all computing equipment that can access a network be required to have a DRM chip. And then set conditions such that the Linux hardware world wouldn't be allowed to obtain one. The government may not (currently) have the legal authority to simply stop someone from designing and building an open computer. But they can prevent them from selling or deploying it of it doesn't conform with some other crazy law.
And lest you think it impossible, look at what happened when manufacturers attempted to introduce DAT tape recorder/players to the US market. Media franchises raised such a ruckus, and so much pressure was placed on importers and distributors, that DAT was effectively blocked from US consumers - despite the fact there was nothing illegal about owning or using one. Not that it didn't stop the recording industry from spreading widespread FUD through a disinformation campaign that it somehow was
illegal. And it worked. Virtually nobody in the US would sell you a DAT tape system "just in case."
Of course once hardware is locked - and alternative platforms prevented from being deployed - then you will only have your choice of Microsoft, Apple - or everybody's favorite Judas: Google/Ubuntu.
Figure this will happen within the next 10-15 years since they've already 'educated"' most of our next generation to 'not care' about any of this.
Nothing sadder than seeing a genuine mechanism for liberty and freedom get crushed by corporate greed on one side, and public indifference on the other.
So it goes.