VDL4 as an ADS-B datalink will not be used widely in Europe other than in certain regions like Sweden and Russia.
The main thing about ADS-B is what you can do with it. The US is already putting in a network of ground stations so they can eventually get rid of secondary radars. Europe will likely follow but plans here don't seem to be as firm.
A huge benefit will be airborne applications using ADS-B (a.k.a. ASAS). Again the US is leading here, e.g. UPS at Louisville.