There could be a script of some sort that gets the latest build and downloads it. That's a good idea.
Dear titaniumtown,
it is nice that you think this to be a good idea but actually it would be in conflict with AUR guidelines as this is not a package with a git (or equivalent) suffix. Hence, automatically building from the current HEAD would be against the AUR guidelines. However, feel free to upload such a package with the addition suffix. Note, papermc actually has a git repository from which the software can be build so it is absolutely doable.
Since you have not mentioned or taken written note of any of my criticism about your request, I would like to again remind you again that an orphan request is an awful way of engaging in this kind of discussion. Please think about my previous response.
Best regards,
Gordian