Multiple hotends/toolheads thoughts

This is an idea I've been thinking about for what amounts to something like a simple mill tool changer but for printers.
The idea would be to run multiple bowden tubes and line the heads up in a rack on one side, of the print area, you could probably even use a single extruder motor, with something like a simple solenoid to determine which bowden tube was being driven.
In the sketch below, the grey part would be the "carriage" (drawn small here to make it easier to see the other components), the slot is narrower than the circular hole in it, the carriage approaches with the purple clamp held down against the spring by something, as it reaches the center the clamp is released and the spring forces the hotend's wider diameter into the hole in the carriage, providing a hopefully accurate location.

This probably makes more sense with something like a rostock, where vertical speeds aren't severely limited.
Given the minimal loads involved the spring ought to be enough to hold the hotend rigidly, and I think it ought to be possible to clamp and unclamp the hotend just be moving the carriage.
I'm mostly thinking about this for separate support extrusion, without having to drag two hotends around dribbling plastic everywhere.
Obviously there would be a print time penalty for the tool change which is likely going to be in the 10 second range even with a fast moving printer.

Anyway just throwing it out there, to here other peoples thoughts

This is similar to the idea I mentioned here: [forums.reprap.org]

The difference is that I think you should carry multiple dies/nozzles around one horizontal axis cylinder, with internal seals, so that it only extrudes downwards, and you have different sets of nozzles around the circumference.

So the hot plastic goes in from the end along the axis and it extrudes downwards, and there's a motor to spin the nozzles around to switch them over.

You'd probably have to machine the nozzle out of metal or something, maybe aluminium, it's got to be thermally conductive so that it can keep hot.

The point is that you can select a nozzle to lay down multiple beads simultaneously, so it should print manyfold more quickly.

It's a similar idea, the idea is to switch dies over.