Is it possible to remotely terminate another device's session on bitcointalk that's using the same account?
Other than changing your password, I believe not.
I noticed that I can login with my phone and PC simultaneously and also post with the same device at the same time.
Correct.
Would this feature be added on the new forum software? In this way, users can track where are they logged in and to possibly know whether their account is compromised by looking on their active session history. It might be a cool feature to add in the future tbh.
Yes, but this is not the right sub board for making suggestions for the new forum software.