IO540
Right now there is no solution for gliders, the vast majority of microlights, balloons, paras, hangliders and many PFA aircraft. All of the above have either no electrical system or non which will support currant technology transponders. Several of the above groups have negotiated exemptions from the Mode S implementation so no it will never be all airspace users. The “low power” mode S solution is on its third supplier and is not yet finished, so no way could this have happened 10 years ago.
The original mode S emissions tests were done on large metal aircraft. Recent tests on fabric and composite aircraft have found that emissions are several times the EU H&S limit. This report came form one of the Scandinavian countries and is now being looked at by EASA. PFA expectation is all fabric and composite aircraft will be excepted, but this has a long way to go yet.
Rod1