I'm a bit late to the party on this one. I think you can put the whitelist out to community governance - with a small stipend for the governors. As an approximation, five recommendations worked well enough, but now the feature probably needs a bit more automation in support of human based governors.
Removing the whitelist will probably encourage spam and worsen reward pool abuse. With current sentiment towards upvotes services bring quite negative, it probably pays to work with the community more. Having community contribute to governance might help with buy in to MB's services.

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