Thanks to everyone who took the time to answer the polls above. I’ve now closed them.
The first pull-request to come out of this poll is [Drop support for old ocaml versions by raphael-proust · Pull Request #947 · ocsigen/lwt · GitHub](removing support for OCaml<=4.07). This was the cutoff in the poll. It removes a lot of #if preprocessing statements and a few workarounds to stay compatible with old Stdlib interfaces. Thanks to @hannes for contributing most of the commits on this pull-request.
If support for OCaml<=4.07 is important to you, please participate in the pull-request’s discussion or on this thread.
Stay tuned for more. (But also be patient.)