The Foundation as a fiscal sponsor is an interesting question I’m not currently qualified to answer. 
If you know people who feel like they are at a point in a given GNOME project where funding is what is needed to take the next step forward, I would appreciate speaking with them about the project(s).
We’re also trying to collect “fundable projects,” which are projects that are in that place: where they need funding to move forward, and have concrete plans and steps ready to go once funding is secured. There is a wiki page where projects can be added: Fundable Projects · Wiki · Teams / Engagement / Fundraising · GitLab. When we see grants that match projects, we’ll be able to apply for those grants.