Well, I think that the above posts stating that a turbo for the Zetec would take off, are right.
The main reason? Two words: Focus Resale Value and Used Market.
The Focus, I feel, will take off in a few years the way economy Hondas have. These are cheaper off of a used car lot. You can buy a 15 year old civic for the same price you can buy a 3 year old Focus. Price related to "newness" is attractive to young kids wanting their first car.
Also, Zetecs are the predominant engine, and many people w/ Foci have children (not just our current Jetters, either). That is a market that, in a few years, will possibly want to tune the car mom and dad let them drive and which will eventually be their own car.
I think to stop working on parts for a discontinued engine may not be the best idea. Of course, I'm sure FS guys watch the cost of mass producing these parts compared to average monthly sales (or whatever) to know better than I, but look at how many cars have many years and many miles on them and are JUST NOW getting modified.
BTW, I could care less as this whole thread doesn't apply to me unless it'll fit the Mazda 3. If it does, we'll hold off on the supercharger and get the FS turbo.
Yang