Offhand, my first thoughts would be Marco d'Itri (who deals with many low-level system packages with long histories, as well as things like inn, and some code around Berkeley DB which sometimes uses existence-based lockfiles) or Chris Hofstaedtler (likewise, notably things like util-linux and shadow).
The tricky thing is finding packages that use existence-based lockfiles, as opposed to file locking (e.g. flock). One of the reasons for making this proposal is that that practice seems *almost* extinct at this point, with the notable exception of some serial device locking or mailbox locking. https://codesearch.debian.net/search?q=%22LCK..%22&literal=1 might help.
