Its the usual DBA answer of "it depends", it all goes on how the infrastructure will be built and how you want to do HA/DR

As with anything as complicated and as legal binding as licensing, I always detail to speak to Microsoft or your re seller to get it from the horses mouth.

In our setup, all hosts in both DCs are licensed as we use 3+ node Always On with read only secondaries so we serve data to all applications from each DC as we run an Active/Active DC setup.