[amluto]

16 million is way too few because of collisions and the birthday paradox. Even with a tiny corporate network, you are likely to connect to other companies’ networks, and, with private addresses, no one coordinates allocations. Collisions are quite likely.

Also, the major players probably have more than 16 million devices, especially if you could VMs.

[yyyk]

Every sane large internal network is segmented. I doubt all the "more than 16 million devices" need to talk to every other device. The IPv4 limit is an annoyance, but not a big one for the typical internal networks.

[amluto]

When my internal network connects, via any non-NATed means, to a vendor’s internal network, there is a chance that my addresses conflict with theirs. If the vendors have even a few tens of clients, this risk is quite high.

[enkid]

This is especially true because people tend to use the same private addresses over and over. How many devices are 192.168.1.1 vs. 192.168.52.123 ?