then i thought of turning length= into a function that takes &rest arguments and each argument can be either an integer or a sequence. you can find the current implementation at the end of the mail, but i'm not sure vetoers will like it... it's somewhat dwim-ish in that it accepts both integers and sequences at any position, but on the other hand anything else feels crippled from the user point of view.
final call for vetos for length=...