On the user side you need to:
- pay the service a recurring fee
- pay the client probably a recurring fee (x2 or x3 if you use multiple clients on different platform)
- mix and match the above and manage when it falls out of sync
It's totally possible, but how many users are willing to go that route ? Weather apps could be an example of that with the pluggable data sources, but that's to me a crazy small niche.