I think it's time to sum this discussion up.
My proposal for this challenge would be as follows:
Film type - color and/or b&w ok, could use either or both during the month.
Shooting/Posting - there were a lot of ideas on this but the one, for me, that is the most inclusive is to shoot every day during April and post one image per day in May. So from what you shoot on April 1st, you would select one image to post on May 1st. As May has one more day than April, May 31st would be the day for whatever you want to post.
Images will be posted on a separate daily thread (different from the digital posters).
Posts should include basic exposure data, i.e., f-stop, shutter speed, ISO, camera. Extra credit would be to include data on film development and/or scanning used.
Lens - as this still is a single in challenge, the constraint will still be to shoot with and use images from the same lens during the month. Different camera bodies are ok but the same lens is to be used during the month. That means...you could select a 6x7 lens and shoot with it on a 6x7 camera, convert it to 645 or 35mm and still use images from it. That might be an extreme case but that's ok as far as I'm concerned.
In looking over this discussion I feel that some understood this to mean shoot only one image per day. That is not and has never been the rule in this challenge. You can shoot as many images as you like each day but you will only post one image per day.
I hope this gives maximum flexibility to all film shooters here. It's a bit funky to post a month later but that should be plenty of time for all to shoot/develop/select/scan/post their 'Single in April film only Challenge' images.
That's my take. How 'bout it?