I am only guessing, but I am sure it is on route into a SRU soon. Python 3.7 was added in SRU 12.5.0 and I guess more modules will come available as they move away from Python 2.7.
You can check the current python-ldap status at solaris-userland https://github.com/oracle/solaris-userland/commit/8d67f5be617942b1d61c6fa956b4ade0215ee3d9 which shows it was include in Oct 26. Naturally when it will appear in a SRU is another question, but I am sure soon.
You are right about Python 3.7, but Python 3.4 in available as IPS package since 2015: pkg://email@example.com,5.11-0.175.3.0.0.30.0:20150821T171714Z....
From the other side Oracle still heavily use Python 2.7 so for sure it will part of the OS for a very long time.