I know that this could be hard since snap! is a inspiration or Scratch but for my new game coming soon maybe 20MB to 50MB at the minimum for file size or maybe 60MB to even 100MB at the maximum.
It might not come for awhile but maybe sooner or later a bigger filesize would help everyone who wants to make bigger games/projects
Or, if projects are gonna use a lot of repeated assets, use an infrastructure like Scratch and store the assets separately, storing by hash and then reference that in the project data instead of a base64 image url. That way each asset only has to be stored once.
And if unused assets are gonna be an issue, we can always do periodical cleanups.