Having the trailer provide a significant percentage of the propulsion might make for some tricky handling characteristics, especially in slick conditions. You could put all sorts of sensors and computers to improve the handling but that really drives up the cost.

Perhaps a better approach is to build lighter trailers that can be towed by smaller vehicles. My boss recently bought one and loves it. You're right that the normally constructed trailers are often so heavy that they require a really big tow vehicle. His trailer is over 20 feet long and can be easily towed by a small Toyota pickup. Improved aerodynamics would probably help, too.