Considering that Marty is both the author of the format and the emulator, I can't imagine it taking long for Nestopia to support it once it's finalized.

My thoughts on checksums: The format should be flexible so newer fields can be added when needed. You can have CRC32, MD5, SHA-1, SHA-256, etc. Programs should ignore unknown fields (maybe give a warning message about the unknown field (since it might indicate a spelling error), but not remove it). This gives increased flexibility at the user's needs. The emulator probably should check at least CRC32 or MD5 (user configurable is optimal) on load so the user can be warned about corrupt files, though I can't imagine it preventing bad ROMs from being distributed since all the malicious users need to do is update the checksum fields.