I think the point is 'convergence devices' currently have 0 decent choices (as far as I know anyway), beyond dual-booting. Let Android / IOS / MS take that market, and you might look back on the idea of having Sailfish / Lipstick there rather fondly...

A Linux with a closed source UI for tablet type behaviour, with the rest open, would be a perfectly acceptable compromise for many for now. Especially as the long term goal seems to be to open as much as possible.