As I understand from the proposed implementation, other apps could participate in the reward pool and subsequently draw a part of it towards their own ecosystem, by using their own splitting schema. Think busy.org, with a different reward schema.
That's what I understand from Multiple Arbitrary Split of the Rewards Pool.
The Multiple arbitrary payout feature is a way for website like busy.org to receive a percentage of rewards earned on their platform but the distribution ratio issue will still be there.
In my understanding all content will compete for the entire reward pool, regardless of its source (steemit.com, busy.org), and the rewards are split differently according to each source/site algorithm. The distribution ratio may continue to be a problem in Steemit.com, but busy.org will have a different algorithm. That's what I understand, but I might be wrong.