For a long term perspective, It would make sense to have MSFS online service as a subscription.
If I recall, MS already stated that they will continuously improve and provide support for MSFS 2020 for the next 10 years (from release date). I hope the online service would be free at least until 2030.
BTW. By that time, perhaps there would be a brand new MSFS 2030 released and the online service would also be free for the next 10 years… who knows…