Adjustments to Gridcosm would likely be done via a "spin-off" project, or a separate "reboot". For instance, I'd be curious to see a Gridcosm that had a severely limited (8 colors) color palette, or a Gridcosm that allowed only one piece per user per level, or a Gridcosm made up of triangles instead of squares (only 3 new pieces per level). Etcetera.

Realistically, though, hogging is never going to stop unless it's a technical rule change, and that might not even stop it. Determined hoggers will just create multiple accounts (as I suspect they have in the past). Whether through misunderstanding, contrariness, egotism or simple aesthetic preference... people are going to "expand to fit the space available" with their art.