The good news for FOSS is that hosting costs just keep getting cheaper, so providing free SaaS is increasingly feasible.
There’s also the “third way” of FOSS with a hosted option available. Wordpress is a good example of that. If deploying such projects on the cloud eventually becomes trivial, then you could imagine a FOSS desktop in the future might have a cloud component (or be entirely remotely hosted). That might sound odd, but consider you still need to buy hardware to run your FOSS on, so renting that hardware instead isn’t a great leap.