Data-link clearance trials have been going on for some time in Europe. It would be an improvement clearly. But on a busy frequency, the concern is that we may be unable to interject with a safety critical message, for example a TCAS resolution.
Whilst I might be broadly happy to accept the increasing use of ‘negative handovers’, ie the assumption that an aircraft will have arrived on a frequency without a formal check-in, this would have to be backed up by vigorous protocols. For instance both pilots should cross-check the frequency has been correctly selected, and that the traffic on the new frequency involves the expected stations. 121.5 must be monitored in case the frequency hand-off was erroneous. This procedure might be suitable for some ground stations such as Apron, Tower, and en-route sectors, but it is unlikely to ever be suitable for a TMA/RAPCON controller.
Still more reason for us all to strictly adhere to RT discipline.