I have just finished a first version of dynalist-archiver, a Node.JS module that can archive finished tasks from one document to another.
The readme file linked above (hopefully) contains all the information to get started.
You can configure what attributes mark a task as “done” in your setup (is checked, has a @done tag, …), you can modify items so they look good in the archive (remove checked status, remove color labels, …), you can group items by date or anything else you want.
It’s currently just a Node module so you will have to write some code yourself to get it running. But I am working on an example project that can be easily copied.
If there are any questions, feature requests or general comments, I’d be very happy to hear it all.