You are right that there have been people speculating about it for a long time, going back more than a hundred years. Some of the earliest reports are from the time of the Indian Plague Commission, and there have been some snippets of evidence since then.

One of the groups that is doing most of the research on body lice as vectors of plague is the group of Didier Raoult. Michelle Ziegler made a nice summary of that work here:

https://contagions.wordpress.com/2016/11/17/the-case-for-lou...