It's exceedingly difficult to get traction and buy-in. As a freestanding effort, all but impossible. I'm holding out hope that as a side-gig / loss-leader (that is: rather unlike Purism's model, unfortunatley), it might be tractable.
Keep in mind that Microsoft and Facebook failed at this. That former industry giants Nokia and RIM were felled. That Sony Ericson is no longer free-standing. Palm has died.
It's a ruthlessly competitive market with huge winner-take-all dynamics. Apple and Google are the current incumbents. History's lesson is that they will probably fall, but only to be replaced by equally oppressive monopolies. This to me is not progress.
Apple and Google will only be replaced when there is a disruptive innovation in the hardware form factor. Maybe AR goggles or something like that. As long as we stick with flat rectangular mobile devices there's just no room for other major competitors in the market.
Innovations have come in service coverage, quality, pricing (flat-rate, unlimited calls, is now the norm), early app phones (Palm PDAs making the transition), integration with corporate email (RIM), Web access (from early on, but Apple made the breakthrough), and what really underpins the present mobile devices world: advertising.
It's the fact that Google can haul in about $100 billion a year in ads sales that makes Android viable. Apple is profitable on hardware, but even there, struggles to match in technology (though it's vastly ahead in UI/UX), and has a small fraction of the market of a niche it had created.
Microsoft lacks the ads tie-in, and faces obstacles to positioning itself as sole gatekeeper to its remaining desktop / enterprise software empire (practical, political, legal). Amazon's strength might be in leveraging devices as extensions of its storefront, but that's precisely the aspect of its devices that I found so off-putting. They've all the warmth and personal appeal of a third-tier shopping mall. Though if the company can get that right, and avoid Microsoft's 1990s antitrust experience, they're a considerable competitor.
Facebook's failure may be due to growing distrust of the company and of its second-tier status (after Google) in ads. There's not enough draw to the device, and not enough revenue to support development.
What opportunities this leaves for new entrants is an open question. It also raises the issue of Purism, or any other pure-play device firm's, future. Almost certainly aquisition by some party which is tied to a revenue or related-services or -systems model.
Given the incumbents, my bet would be first Amazon, secondary, if it is truely embracing Linux, Microsoft. Though there might be others. I discount Google or Apple. Facebook is a possibility, though given Purism's focus on freedom and privacy, would be fatal.
Outside the US: most device manufacturers are too strongly wedded to one of the incumbents to make a plausible play as this would imperil their Android or iPhone contracts, which would rule out Samsung, Sony, LG, etc. A non-US telco aquisition, possibly in Europe guided by privacy regimes, could be an option.
On reflection: focus on form factor is almost certainly a red herring. Look to the sustaining business model and positive/negative appeal factors.
Keep in mind that Microsoft and Facebook failed at this. That former industry giants Nokia and RIM were felled. That Sony Ericson is no longer free-standing. Palm has died.
It's a ruthlessly competitive market with huge winner-take-all dynamics. Apple and Google are the current incumbents. History's lesson is that they will probably fall, but only to be replaced by equally oppressive monopolies. This to me is not progress.
I'm hoping Purism does succeed.