This is one I've tried several times to figure out, as well as work around. This is the missing functionality that has made my other team members give up on Trello. We would love to find a way to add the same checklist to all (or multiple selected) cards simultaneously.
My current workaround is creating a Template Card with a Template Checklist, and individually opening every card and copying the Template Checklist to each card. The nature of our projects means that our boards typically use 100+ cards, so this is an immensely time-consuming process.
I've looked for expansion programs that would enable this, but haven't found one yet.
