Most of the companies behind it (including NextCloud itself & IONOS) are providing a document cloud to their users already & are used to maintaining Open Source, so I would indeed assume some seriousness here.

This is much bigger than subsidies. IONOS is already making serious money in selling "we host FOSS for you" to both users and (though generally: small) companies. They can expect to gain substantially greater revenue from acquiring larger commercial and municipal/federal customers.. IF the full package attains sufficient interoperability to withstand the usual anti-competitive tactics.

Both, I imagine

IONOS and Nextcloud are serious companies.