Couldn't you just dial back to a lower service tier than 3-at-a-time? Half a loaf is better than none, surely.
I'm on the unlimited one-at-a-time plan, and that's going up $1 per month, which isn't that bad. However, I'm annoyed that the only cheaper option I've been offered is unlimited instant viewing but no DVD rentals. I don't have the bandwidth for instant viewing to be practical, so I wish they'd offered me the reverse: a cheaper plan that's all DVD rentals and no instant viewing.
I'm on unlimited one-at-a-time, too, so I obviously agree w/ your suggestion. A lower/cheaper plan is much better than none. I love Netflix.