Will confirm soon

I'll get started on that (probably start by editing Petra, neve made a whole bot before) sometime soon, and see what I can come up with.

Well you could make a more friendly one and a more hostile one, then there would be three bots. A bot that better scales with difficulty settings might be another path. Petra has design limitations, you better create a new one with Petra as a guide only. Writing bots isn't easy but if you want to give it a try and it's fruitful then a lot of value can be added to 0ad.

If I were to make a more friendly bot and post it here, could it be packaged in the game? And then we can start improving Petra to be more challenging and realistic?

Petra is in maintenance mode, unlikely to get new features or at least not anytime soon. A bot can be created as a mod, such a bot could be bundled with the main game alongside Petra if it is mature. Keep in mind, Petra is generally considered to strong for new players, a newbie friendly bot could help getting more people into the game.