If you've not actually heard of MonoGame you've likely still played something originally created with it including the likes of Bastion, Streets of Rage 4, Chasm, FEZ, Axiom Verge, Stardew Valley, Tooth and Tail and a great many more (although some moved to FNA). That's just a few taking from their limited showcase page.
As for what they're planning: a lot! They're going to create a non-profit foundation, to ensure it remains open-source and free for all users. Their statement in full:
In the light of the recent news in the game industry and to reassure the community about our commitment, the MonoGame Team would like to share its future plans. The team wishes the MonoGame Framework to become future-proof, both from a technical and governance perspective.
This new era of the open-source project will see the creation of a non-profit foundation to which all rights and properties will be transferred to, with the aim of ensuring MonoGame remains open-source, and free for all and any scenario, including on consoles.
This foundation will allow the adoption of a more sustainable model and will open MonoGame to be supported by more patrons. A new board will be created within this organization with the task to define which projects to undertake, and how they may be funded, transparently.
We will discuss the roadmap at a later time, but we can already state that MonoGame’s goals will be set with regard to the quality of developer onboarding for the framework, its stability and console support of the current version, and the start of a new iteration to further expand MonoGame’s reach and capabilities.
We will communicate the progress of this transition based on developments in future announcements.
We look forward to everyone joining us on this new and exciting chapter.
The MonoGame Team.