Apple has IMDF, it's a way to define the layout of a building. It can only be used in, or overlaid on Apple Maps. That's vendor lock-in. It's not a bad platform to be locked into, it has billions of people's attention. However it's still not great to be controlled by another company, that's why I think you should add the data to OpenStreetMap.
OpenStreetMap is a open platform, nobody controls how the data can be used. It's a great place to store the data as a backup for if one platform oversteps it's boundaries. There is already an open client that displays indoor maps, anybody's indoor maps, indoorequal.
Once you have collected the data for IMDF, there is really no reason not to publish that data in as many places as possible.