Not enough aircraft will be equipped at the original deadline
In an interesting but not unexpected move last week (april 22, 2020) the European Commission and EASA published an amendment to Implementing Regulation EU No 1207/2011 that effectively delays the mandatory retrofit of aircraft with ADS-B to 2023. It turns out that not enough aircraft are expected to be equipped by the deadline.
The original plan was like this:
Every aircraft that is flying IFR faster than 250kts or that is heavier than 5700kg must have at least ADS-B out
Implementing Regulation EU No 1207/2011 Surveillance Performance and Interoperability Implementing Rule, SPI-IR