Trello – Can’t find how to filter Trello cards but keep showing the other ones slightly grayed-out

I agree with your friend about not dividing up into separate boards by type of job.

With your examples such as 'Design ideas' etc, I think they really do fit naturally within different lists on the same Board. It's exactly the sort of usage that Joel demoed in multiple videos about Trello.

The only thing I can think of, to help manage very long lists, is to use Trello's Labels system to put categories on cards, and then use filtering. You should definitely give meaningful names to the default labels.

I wrote up some tips on how to use labels recently.

Having said that, fairly early on the Trello on Trello board got huge, and eventually they reduced the scope of it. So it's does seem to be a well-known problem.

They will be unassigned from cards, and that's about it. Their actions will be preserved, as will the fact that they performed the actions.