I suggest M2W - I couldn't find an existing extension matching that. It's minor, but allows for possible future capabilities such as simple importing/exporting Maps to/from Worlds. In this scenario, maps might have the M2M extension. Additionally, I'd set my IDE or NP++ up to handle/autoformat M2W as JSON (the existing format).
This is a good idea, making MUD Map files more distinguishable. Also, map export (which I imagine as world files stripped down to a single map, omitting all unused values/relations).
I suggest M2W - I couldn't find an existing extension matching that. It's minor, but allows for possible future capabilities such as simple importing/exporting Maps to/from Worlds. In this scenario, maps might have the M2M extension. Additionally, I'd set my IDE or NP++ up to handle/autoformat M2W as JSON (the existing format).