Interesting idea
I think the cost estimate is way out, though, and far too high.
With current elecronics, all units could be built as "standard" units, and just laid over the surface of the taxiway, not embedded. Would only need to be half an inch thick, presumably not enough to worry/damage the tyres etc. The units could be simply secured at either end, locked into place, making changing faulty units a five minute job.
The elctronics could be simlified, and run off a single 2 core cable looped around the place inside existing ducting, that would cut down the holes to be dug.
I know you probably wouldn't want another screen in the tower, but a simple computer interface would allow you to draw (on the screen which was displaying a map of the layout) a route from landing runway to gate, and have the system protect against any incursion of that route, not just runway incursions.
Only drawback I see would be superimposition of the warning on existing communications- sods law says it would happen just as you were trying to get some important piece of info across, but I am sure there is a solution.
Don't laugh, but I used a similar system on a model railway to track trains!!
[ 16 July 2001: Message edited by: stickyb ]