I don't think this is likely, because we don't run into advanced AI civilisations either. The paper says it's because the AI would have different goals like imp

I don't think this is likely, because we don't run into advanced AI civilisations either. The paper says it's because the AI would have different goals like improving efficiency, but you can only increase processing power by being more efficient to an extent. At some point you have to get bigger. Also, at least one of these superintelligences would be focused on getting bigger for whatever intrinsic goal it has, right?