Well, Windows-supporting hardware is cheap. Raspberry PIs don't have the processing power to run anything more than basic HTML pages. Finding 'cheap macs' is a losing battle - Apple hardware holds its value. Running Linux on a display-ware system with a fancy video card relies on drivers for that fancy video card, and there aren't any.
This would be much better reordered. The lead 'why concatenative programming matters' is only answered halfway through, after the reader is expected to trudge through lambda notation. Why it matters: it's the basis for interpreters of languages you use. Then explain why, then explain what it is.
For some audiences I'd agree, but I think the current presentation works well if the target audience is people who already believe that functional programming matters, but are skeptical that concatenative programming is an interesting or important concept. For that audience I think the presentation starting from the familiar type-signature notation is effective.