In short, the reason why Gallia hasn't done, isn't doing, and won't be doing half or more of the things in this thread is entirely because of gameplay-related reasons.
Kusari players and the storyline devs (understandably) don't want us interfering in Kusari during its new civil war arc. Bretonian players don't want to have their entire House go into exile, and the less said about the privileged position Liberty enjoys as the main 'protagonist house', the better.
A whole lot of the stuff suggested would be something I'd personally enjoy seeing, but I'm also well aware that certain others who would be affected greatly by their implementations have an entirely different position on things I'd like to see happen. Having Kusari become an actual vassal/satellite state of Gallia and taking control of its foreign policy is something that I think should have happened from a story perspective, but I can see why it hasn't happened from a gameplay one. That said, in my headcanon Kepler and Galileo should have already become warzones.
With regards the whole issue of Rheinland, I brought a very similar proposal of assistance/cooperation/informal alliance up to one of the previous [RM] leaders, and was promptly told by him that the story devs had intervened with him in private and told him that it wasn't going to happen. Go figure.