I don't like it because it's biased. You might don't see it, but let me explain:
Since the most important asset in torrenting is your connection speed, if you have a reliable high speed connection you have seeding preference. That means you're being rewarded for something that's not a merit of yours, you are just expecting the system to reward you for doing the bare minimum which is to keep seeding your downloaded torrents.
What I think would be more fair in some sense is to reward seeders who are the only connected peers of a specific torrent. Let's say there's a torrent that was uploaded a year ago and you are the only one still seeding it, that makes you actually more valuable to the community overall.
Once someone requests a re-seed, the system could check how many people are actively seeding and if that number is below 3, let's say, it activates a upload multiplier bonus, this way whoever starts seeding that torrent in the next hours get either double or triple de upload amount or a fixed seed bonus reward based on the torrent size instead of the seeding hours.
Buffing the sbp multiplier woudn't be a good idea because it could be exploited by limiting your bandwidth to keep seeding for longer.