Fvwm ran exactly that way on my Pentium-60 and I do not recall ever experiencing performance or latency issues; matter of fact, my Linux desktop of the time was more efficient than Windows. The FvwmPager, FvwmButtons, and FvwmTaskBar modules are separate programs launched by fvwm and communicate with it via IPC. Sacrificing modularity to avoid performance issues that were hard to see even on machines from 30 years ago—let alone on today's hardware—is a bit penny-wise and pound-foolish.