For what's worth, I don't have a dedicated Pause key either, but I'm using simply the Space bar, without Shift. That's actually one of the first things I changed when I started playing 0 A.D.

For what's worth, I don't have a dedicated Pause key either

(Actually Fn+P is the Pause key substitute on my machine, but the Space bar is more convenient for me.)

The spacebar is more convenient for me.

I like the idea of the spacebar in single player games as well. In MP games, there may be many false pauses by people using the chat menu.
Shift+spacebar seems more like a safe way to avoid this and get to the pause menu quickly.

Also, the space bar may be better for locating events.

The point is, one can already insert e.g. hotkey.pause = Space in their local user.cfg file and in A24 they can also modify hot keys from within the game, so I don't really see why it's necessary to continue adding multiple equivalents. (See also line 11.)

there may be many false pauses by people using the chat menu.

It doesn't interfere with chat messages. You can try it yourself.