I wrote to my MP asking him to intervene to stop this silliness until someone has PROVED that GA needs Mode S, and that ATC will really use the information.
I got a load of twaddle back from the Ministry, telling me that Mode S is needed for TCAS (wrong! Mode C works just fine) and that GA was consulted. I've not yet managed to find anyone who thinks he/she was consulted - just a few who were "told" this is the way it's gonna be.
Mode S in its basic form does two things in a GA aircraft (compared with Mode C):
1. It provides more detail to Mode S enabled ATC radars - but there's only one of those so far, and when there are more, the Controllers will have to filter it all out again to avoid cluttering their screens beyond readability.
2. It enables Eurocontrol to know when you're flying so that you can be sent a bill for use of airspace. You think the air is free, and ours? WRONG!
You think VFR flights won't be billed? Want a bet?
You have about two weeks to write in and object. DO IT NOW! There's good information on the AOPA website to craft into a suitable letter.