BW, there is a great difference between “ nothing would prevent” and “ have to”, as I’m sure you must be aware.
What I meant was "In order to detect gliders I have to carry a completely separate bit of kit...", not that such a thing would be mandated. The point was that there would be a proliferation of incompatible standards.
I have better things to do than spend time on a fruitless dialogue.
I've obviously wound you up which was not my intention, sorry: it's evident from your past contributions that you take a balanced and logical approach. Nevertheless, I would maintain that
a) in collision avoidance systems, interoperability is crucial, hence common standards are paramount
b) there is no technical reason why a 1090ES certified system would be more expensive or more power hungry than a certified FLARM system of equivalent range -- the reason FLARM is cheap and light is that it is uncertified and shorter range.
c) 1090ES is
the established ICAO standard
Therefore the sensible way forward for all airspace users is to rally around a light and affordable 1090ES-based system that is proportionate in its cost and power consumption to the class of aircraft in which it is to be used.