The 7-day limit is a problem because any of the videos on youtube go ignored for a long time, and then boom, they go viral, giving the creator a possible revenue stream. As such, the 7-day limit disincentives long posts (more profitable to split them up), and denies benefits to anyone whose content goes viral long after the post. I think if this isn't fixed on the base protocol, or through SMTs, then we'll trend toward more low-quality content.
Rather, I think that perhaps there would just be a lower weight for older content. That way, the system will still promote new content creation the most, but can still benefit viral posts/content.