Hmm... Hard to say. I think you may have trouble differentiating your product with this description. When I hear "persistence as a service" my first thought is "I can just use RDS, or maybe something like Firebase. If those aren't suitable, how hard is it to spin up my own instance of (Mongo|Postgres|FoundationDB|ExistDB|DB2|Oracle|SQL Server|CouchDB|etc) in the cloud?"
Of course the fact that RDS, Firebase, etc. exist suggests there is a need for persistence services in the cloud. I'd just be curious to know how your thing is different/better than the existing alternatives?