Unlimited time-frame reward is hard to implement in STEEM blockchain since every block/reward is produced in a timeframe (e.g. 3 seconds). Reward is calculated from yearly fixed inflation rate.

However, monetizing great contents with online Ads can be implemented with an SMT.

For example, a separate website/DApp for the contents will have embedded Ads according to popularity. Content creators may have to post content using the DApp to participating in the extra earning through SMT. The DApp owner can accumulate these Ad profits and share with the content creators according to contents popularity.
The number of visits can be converted to a number of SMTs for every week/month.

Moreover, extra earning from Ads will attract authors and can also be used buy back SMT's .

Though it looks like it is against STEEM's philosophy, but these alleged ever-green contents need to rewarded forever.

The bottom line is that a top content can earn forever with Ads, however, STEEM blockchain can't reward them beyond 7 days. An SMT with intelligent algorithm can solve some of the issues.