It would give a kick, definitely. I'd like to see that as a user, but not so sure as the maintainer: increased support requirements and complications, lots of devices with possibly half-baked implementations, kernels, etc. The RPi is a well controlled and reliable ecosystem with only a few variations.
The point is not in making the current moode authors maintain multiple platforms, but in modifying moode to support configurations for multiple platforms.
Moode github repos show the project has two parts. The moode builder
https://github.com/moode-player/mosbuild, and the actual Moode layer over raspbian
https://github.com/moode-player/moode . Raspbian is (currently) 32bit debian 10 with rpi kernel (patched mainline kernel). Moode may contain some closed-source arm32 binaries but the authors would certainly know. All other binaries can be recompiled for aarch64 plus moode itself will likely convert to aarch64 anyway as the 64bit raspbian is already being tested and works very good (at least on my rpi4).
RPi is not any special arm board, the rpi kernel just contains a few extra drivers for RPi-specific DAC boards, provided by their vendors. These drivers are listed in moode/build but that could be part of the customization for RPi. On the other hand, new multichannel DAC boards would be in the other platform customizations.
Most RPi-specific issues are not tied to the HW platform itself, but to the specific version of raspbian.
https://github.com/moode-player/mosbuild/blob/master/mosbuild.properties https://github.com/moode-player/mosbuild/blob/master/mosbuild_worker.sh . IMO in many cases the scripts do not need to read exact package versions, in other cases the version can be moved to a platform-specific mosbuild-XXX.properties file. E.g. mosbuild-common.properties (with most values as armbian and raspbian based on the same debian version will contain mostly same packages) + mosbuild-rpi.properties maintained by the current authors and mosbuild-XXX.properties maintained by maintainers responsible for the respective ports. No rocket science, it's just a few bash scripts.
Once the mosbuild script modifies the stock debian installation, the actual moode will run identically on any arm device.
IMO such a project would be quite useful for the community, if Moode authors agreed to this direction. Maintaining the platform customizations may not be so laborious, once hooks to the common underlaying project were implemented. On the other hand forking moode as is will not work without huge maintenance effort. Every merge from the upstream moode branch upgraded for new raspbian will likely cause lots of git conflicts.
I cannot imagine any skilled developer would volunteer to the dull effort of maintaining the fork and voluntarily submit himself to directions of the "steering committee" here. But I may be wrong, yet have not seen anyone like that here or elsewhere. Unless some money is on the table which goes back to my initial question of the project's purpose.