The ability to cumulate both the checklist and numbered modes would seriously improve my life 
I need it a lot for processing feedback from my clients: we use numbers to unambiguously identify items, and each element is a task for me to fulfill. I couldn’t find another practical solution.
Otherwise, Agenda is pretty amazing, please keep up the good work!
Do you mean somehow have a number, plus a checkbox on a line?
The main problem I would see is that the numbers would change when you insert/delete items. I think you would be better to simply enter the number on the line, as text or a tag. If you have the tasks in some other system, you could even copy a link in, so you can jump straight back. I do that all the time — copy in a link to relevant info.
Drew
Indeed, that’s what I mean.
You’re right about the numbering changing with new items, but it is not something I mind — since I don’t add other items in these (sub)lists.
Links do work, but I’m not a fan of that workflow (or similar ones) because it’s slightly less efficient with all the jumping around (and additional work to create the links) — especially for big lists of relatively small items. In particular, I usually create the lists by copy-pasting them from an email (with a “1.” format that Agenda immediately recognizes), which is extremely efficient (just paste and it’s done).
Numbering by hand in a checklist is probably the best, indeed. There’s just a minor annoyance when creating the list (from a copy-paste): since the format is understood by Agenda, it removes the numbers when I turn it into a checklist, and I need to re-enter them by hand (not a big deal, but it can take a little bit). And I also really like the cute tiny font in numbering mode 
In any case, I agree this is pretty specific, and probably not worth implementing — too narrow use case, which isn’t enough to justify the more complex behavior. So please disregard this topic 
Another option to think about is using text formatting in place of the checkbox…a good example might be strikethrough. You can use a keybaord shortcut (shift+cmd+X), add double ~~ to the front and back for markdown, or on MacBooks with touchbars you can have strikethrough as a readily available button