Allow email and record rules to filter records from related tables

I'd like to be able to filter not only on the current table, but other related tables during a record rule or email event.

Current Problem: If random users want to get notified when a new location is added in "Chicago", or "Houston", or anywhere (virtually endless number of cities and towns), I have to add each of them separately..manually. This will lead to a HUGE email rule with hundreds or thousands of email rules on one form.

Possible Solution: Allow email rules and record rules to filter records from related tables, instead of only it's own, and should also be consistent in the task functionality. This will allow me to create a new "Watch List" table to let users add watch items to enter whatever value they want to be notified on. Then, only a single email rule would let me filter those connected watch items when a new location is added.

This is very close to what I want, which is to use data from related tables in my email.

come on! pleeeeeeeze do this!