Mode-S enhanced surveillance is not ADS-B (albeit kinda close to it) but requires downlinked rates of climb/descend (BDS 6,0). Enhanced surveillance is by now required in many ECAC states. According to the aircraft list on the eurocontrol site recent MD-80s can downlink rates of climb/descend, just not selected altitude. CRJs can downlink rates as well, just not track angle rates. And EMB-145 can downlink all required parameters as standard. Retrofit kits exist to make those airplanes fully EHS compliant and many operators have fitted them as it is easier than to get an excemption from EHS from each individual state within europe.