might be a bit basic - but a functional coffee cup & fully 3d printed caffitiere is something that would definitely attract attention at tct.

You can't do it with any of the standard filaments.
Could you print a working kettle ? No reason why not.
As long as the element doesn't exceed the metling point of peek, keep it fairly small so it doesn't take all day to boil.

So while not engineering related per-se, a kettle, cafetiere (kind of winging the spelling on that) and coffee cups all printed from PEEK - not only would attract a lot of attention and publicity, but demonstrates a few of the properties of PEEK that do apply to engineering projects.
And I do mean the caffitiere should be entirely made from peek.
Pretty straight forward.

Nobody's done it yet either :-) It's something I'd definitely have remembered.