I don't really understand what are they fixing here. They point that current web development has shifted to "REST backend" and "SPA frontend", which (according to them) is not a good thing (why?). Their solution is to make you write (again) a "full" MVC-backend that also serves the UI (frontend), and additionally, extend it with another frontend layer (Vue).

IMHO that is not fixing the initial problem they are stating that exists, but making it worse, because now you have to write UI-related code in two languages (ruby and js) instead of the 1 that is currently needed (REST + SPA).