@arhag Long-term, surely the required investment you are talking about to maintain the platform will not come from (effective) user subscription, but from advertising: companies buying influence in the form of Steem Power and using it to curate posts in their favour.
This could be directly (ie. the posts they're upvoting are adverts for the company) or indirectly (ie. a travel company might continue to pump money - and impressions - into the already proliferate travel blogs on steemit).