Sure, it’s a terrible idea, but we all know that speed >>> common sense. Rubbing somebody’s rear tire with your front tire won’t end well, but what if you could somehow push the bike in front of you when in a paceline? Your balance on a bike pretty much relies on the front wheel, so we don’t want that to make contact with anything, even if it had some sort of bumper in front of it attached to the dropouts or something.
What MIGHT work is to attach a beam to the seatpost of the bike in front that the rider behind could grab hold of, like an extended seatpost-mounted rack. The “safest” next step would be for the rider behind to basically stiff-arm it. We can finally put our tremendous upper-body strength to good use! It would be very fatiguing, but having the beam that is attached to the seatpost make contact with anything solid on the bike behind would probably end badly / expensively. And if your arm gets too tired, just use your head!
This whole idea would SURELY be banned by the UCI as well as anyone with the least bit of common sense, but I do wonder how much faster this kind of paceline would be. I’m sure someone will throw out the idea of a mega-tandem, but anyone who has ridden a tandem knows that trying to get just 2 people coordinated on a tandem is very difficult, let alone multiple people.