Stuart Chalk wrote on the CHMINF-L mailing list about Open Spectral Database (OSDB). This new database is more of an idea than something with critical mass yet. But the idea seems right: it has a CCZero waiver for the data, is Open Source (see github.com/stuchalk/OSDB), and API. The webinterface looks good too:
It supports various spectral types and maybe it can be seeded with data from one of the Massbank instances. That said, it does seem popular enough to already attract some spamming in the collections corner; that also means, it needs curators that keep an eye on what enters. Perhaps register via ORCID may be an option to fight spam, but I do not have experience with setting that up. Other feature requests I can think of is links out to Wikidata, in addition to the existing three databases.
Now I really have a good reason to dig out my past NMRShiftDB contributions and submit that here (see also these past blog posts about NMRShiftDB).