In Vitalik’s recent talk at the Stanford Blockchain Conference (51% attack recovery), he mentions the view-merge algorithm (47:08), by which online nodes can tell which other nodes are online. This, of course, has implications for a censorship / exclusion attack.
Where is this research at? I wasn’t able to find a paper describing the view-merge algorithm or any adjacent research (besides of course the classic Vitalik ethresear.ch post on 51% attack responses in Casper FFG).