There's actually been significant progress towards interop in the last 10 years. HIEs (Health Information Exchanges) such as CommonWell are steadily improving and covering more patients.

Recently there's been a big push for TEFCA (Trusted Exchange Framework and Common Agreement) as the network-of-networks that federates all the different HIEs. It's been slow, but it's progressing.

As usual, the problem isn't really technological -- it's getting all these different stakeholders, with different business models, etc, to agree on how it should work.