.mojoc and .mojobc are strong contenders
re: mojo bundle
Imo this is too nice a name. Keep in mind that the .mojopkg file is tied to the exact version of the Mojo compiler that produced it. Generating .mojopkg from a mojo nightly from Date 1 and then using it with a mojo nightly from Date 2 is error prone. Name should reflect that fact. Imo, “bundle” does not hint that at that relationship.