Right. We used to do perfectly serviceable work on extremely small screens, sometimes displaying as few as 40 columns and a dozen rows of text, and with keyboards that were so painful to type on that most commands would be abbreviated to 2 or 3 characters. Current versions of Linux still include a "quirk" for supporting an uppercase-only text mode that was common on early terminals and microcomputers. So no, hardware capabilities are not an inherent obstacle here. Providing an information- and interaction-dense UI on such limited devices is definitely a challenge that will require some added work, but the kind of 'convergence' that Purism is talking about is a necessary building block.
So echoes of, but not at all constrained like, computers from that era.