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.

So, after both playing against and editing Petra, I have found several features that Petra needs to really stand a chance against a competent player. #1: Petra doesn't build walls. This is a real problem, since it leaves it open to anyone with some siege rams and a catapult or two. It also means that Petra never really acts like a real player, especially when set to defensive (when it should essentially just turtle). #2: Petra doesn't upgrade buildings or units. I know this is more minor, but it is important, as it means that the closer you get to the center, the weaker Petra is, since it built Sentry Towers in Village Phase (with little territory), then started building Defense Towers in Town Phase (as it spreads out). It would make Petra more challenging if it upgraded Sentry Towers to Defense Towers. This also has another problem: Petra never upgrades units, so it has to wait till City Phase to get the Centurions, when it could upgrade them as soon as they reach Elite Rank. Also, the Mauryan Maidens never switch from their melee version to their ranged version, which is a problem. #3: Petra doesn't turret on walls. While this requires walls (see #1), it is another thing that would be useful to add. I know it is too late to put these into A28, but maybe we should try to implement them for A29?