https://trac.torproject.org/projects/tor/wiki/doc/ResearchEthics
Any number of problems and obstacles to legitimate research areas exist with this...
" Examples of unacceptable research activity
It is not acceptable to run an HSDir, harvest onion addresses, and do a Web crawl of those onion services. Don't set up exit relays to sniff, or tamper with exit traffic. "
Assuming such bans, how is one supposed to legitimately research and report on the real makeup of onion or exit space? These are significant unanswered questions regarding tor use.
Concentrate not on bans, which will be ignored by both legit and illegit researchers anyways, but on proper design for data handling and minimization, particularly being sensitive to the tor users and operators involved lest that data become compromised at any stage before final anonymization and wiping.