Tor will already avoid making circuits where two IP Addresses in the same /24 are involved. The research in this paper (https://www.freehaven.net/anonbib/cache/DBLP:conf/ccs/EdmanS09.pdf) is becoming more relevent and is worth discussing as more ISPs come out with the goal of hosting lots and lots of exit relays.
A valid point, thanks for linking the paper. I have the utmost belief your intentions are good, but the concentration of exits under a non-advertised central control warrants conversation, at least.
If the end goal is turning $ into relays, not all paths are paved with equal mind to security and it might be worth considering donation-backed alternatives.
Have a good one,