I think the point I was trying to make was that by having the connections attached permanently to the cars, you present a couple problems that many cities just wouldn't want to deal with.
First and foremost is the question of clearance. The average Tram car is 12 feet tall, (give or take) with an added 5 feet for the pole. (again this is just rough estimates). However the majority of cities that have surface traffic (trams) would find issues with the system as it stands designed. The reason is because catenary wires are "variable". When passing under a bridge, it's not uncommon for the wire to lower down, pressing the pantograph or pole down with it. This image, taken from wikipedia, demonstrates this with a feeder rail. However, notice how low the pantograph is, compared to usual running.
http://upload.wikimedia.org/wikiped...P1220601.jpg/800px-Overhead_rail_P1220601.jpg With the fixed system as you've imagined, it would limit the use of the cars, since the connection points would prevent the system from passing under certain locations.
When I took the carriage design and revamped it, suggesting a "transition" system, it was based on this problem that I didn't think you knew or understood. In my own design, I expected that the system could be in use well prior to its completion, with the carriages already in place and operating while the overhead track system was being built. By using the slot system also, it allows for greater versatility, since there is only a minimal overhead clearance, meaning that retrofitting of existing tram systems would be much easier. Furthermore, with the removal of the overhead wires, beautification projects can be added, as you would no longer have the eyesore of a series of overhead power lines.
Lastly, when I imagined my own variant of your system, I expected that the trains would operate on a tram type system with a series of stops along the way. Using an existing surface system, the cars would then enter a reserved area where the transition would happen. This would all be done in a station setting, with the "five" minutes or so being taken up while the train was already stopped for passengers. In that, I used the following video for inspiration. This video shows how the Talgo can change its gauge on the fly, without having to stop the train. I expected something similar, though with a minor stop to allow the bottom panels to be attached.
http://www.youtube.com/watch?v=EdOKVFx5Yx0
Lastly, there is one reason why I figured the removal of the bogies would be better. The simple truth is, leaving them in place is much harder to engineer than to use a moderately normal system where they are removed. Keeping them as part of the carriage you present the chance for lawsuit should something fall off the bogies, or the wheelset itself disengage and fall away.
Edit:
One idea I considered in my own design, that I'd like to toss out there to you, also based off the "talgo" break of gauge system, would be to have both the undercarriage bogies and the roof bogies mounted hydraulically. As the operater approaches the change of control system, he raises the roof wheel set, and then once it engages, raises the lower ones. The design problem here however goes back to the final note. First it would be insanely difficult to design. Secondly, there would need to be some way, similar to airplane landing gear, to close off the openings to prevent anything from falling off the carriage and harming someone below. If this could be worked out, then you could continue the design as you invisioned it and change gauge on the fly. However it's something that would require much more engineering than the seperate system.
