Hello shavano,
Thanks for contacting us, this is a neat idea.
Unfortunately that level of customization does go beyond the scope of the forums, but if you have a moment, we’d love for you to submit your idea to our UserVoice forum. We take user ideas and contributions very seriously, and many times their ideas end up in our future releases.
If you were to implement this yourself, I would look how the plugins you describe do it. Off the top of my head, I imagine there is some sort of before-post-is-saved hook you could access, and then grabbing the venue city and tagging it wouldn’t be too difficult. I would estimate 70% research and 30% implementation. Maybe 5 hours tops for dev with time.
Does this make sense? Let me know if I can explain anything else!
Cheers!
– Casey Driscoll