...only 7 days of payout instead of perpetual payout
I generally agree with that this is a less competitive incentive compared to, for example, a recognized author who'd potentially be earning perpetual residuals on a piece.
That said there are mechanisms for rewarding older posts. For example you can comment on a post that's older than 7 days, setting the beneficiary to the original post author. Then vote on that comment. A button to make this more convenient could be built into a front end, if the front end implementer liked the idea of rewarding older posts.
building a way for advertisers to spend on ads around a post could also cause some perpetual income.