Connected efbs need a communications datalink, there is a push to move aircraft away from the old slow expensive ACARS networks into IP based solutions as new generation aircraft just use so much more data, for efbs, for passenger services, for maintenance, and covid. A good barometer for what you are asking would be closely correlated to the WI-FI uptake, as that same datalink can be used for airline operations.
- 70+ airlines worldwide offer inflight wifi in most regions of the globe, with several large global airlines preparing for full or near full rollouts.
- 39% of available seat miles (ASM) worldwide now offer at least a chance of wifi
- US airlines offer at least a chance of wifi on 83% of their ASMs
- Non-US airlines offer at least a chance of wifi on 28% of their ASMs
so my best guess for connected efbs domestically in the US the number would be around 80%, globally around 30%..