Government Overhaul
So for the upcoming patch (to be released soon, we promise!), one of the larger changes (one that we've been planning for quite a while) is to finally split up the vanilla Tribal and Feudal government forms that were never quite a great fit for the mod or the realms of the time period.
First off, we've split the Tribal government in two. The "new" Tribal government represents the rather unorganized tribes of Ireland, Pictland, outer Germania and Scandinavia, which had never seen any sort of proper political organization and would not for quite a while yet - even more disorganized than what vanilla represents with their tribal governments. For now they are mechanically quite similar to current Tribals with a low Tribal Organization law, but with a harsh demesne and vassal limit malus, as well as being unable to build even temple holdings. They can be reformed into the next stage, High Tribal government, similarly to how Tribals currently reform.
The new High Tribal government represents realms still grounded in Tribalism but with a greater shift towards the stability and institutions of feudal/urbanized realms, and are basically a step up from the Tribal government. At start, this includes most of the tribal nations inside the borders of the former WRE, as well as the former Roman client states north of Hadrian's Wall. High Tribals have a reduced vassal and demesne limit malus, have the mechanics of current Tribals with high Tribal Organization, and can be reformed into one of the feudal governments.
The Tribal Organization law has been extended to 7 stages, split between the first 4 laws for Tribal realms and the last 4 for High Tribals - the Medium Tribal Organization law is both the highest stage for Tribal realms (required for reformation) and the lowest stage for High Tribal realms. The effects have been spread out over the new laws, which means that only High Tribals can revoke titles or raise vassal levies. Tribal organization has also been made harder to raise, with prestige requirements and costs as well as a 10-year cooldown.
Similarly, the tribal building chains have been significantly extended; in general, each individual building/upgrade is less powerful but also less costly, with reaching the final tier both more costly and more powerful. As with Tribal Organization, the higher tiers of buildings are locked to High Tribals, who will generally have better developed (and better fortified) holdings.
Your choices of government reformation depend on your culture and situation. Highly Romanized cultures (Roman/Imperial cultures and Romanized Germanic cultures) can always reform into a Sub-Roman government, while semi-Romanized cultures (e.g. Britons, Cumbrians, Vasconians) can reform into Sub-Roman governments if they have a Romanized culture province, a Romanized government vassal, or a Romanized government neighbour. Semi-Romanized Germanic cultures (e.g. Franks) can reform into Germanic government in a similar way. It is possible to reform into the Romanized governments as a non-Romanized culture, but doing so requires you to also have significantly centralized laws first as well. There is, of course, always the choice of reforming into the basic, but generally inferior, Feudal government.
We've also changed how cities and temples are generated during reformation. Temples are no longer generated on reformation, though they can still be built while High Tribal, of course. Cities will now be generated based on the level of your Market Town building chain in the primary Tribal holding. Here you can see that Dereutione has a 25% chance of generating a city, due to the level 5 market in the holding (the lowest necessary tier) - at the top tier, you are guaranteed to get a free city.
So what's different about the Sub-Roman government, used by the various Sub-Roman successor states as well as the heavily Romanized "Germanic" kingdoms of the Visigoths and Burgundians? Well, compared to the Feudal government, Sub-Roman governments are significantly more centralized and despotic, with free duchy/kingdom revokation and vassal retraction. As part of the (decaying) Roman urban culture, they are also allowed to hold cities without penalty. The Sub-Roman Brythonic government, for the Sub-Roman kingdoms of Britannia and Armorica, is similar, but without free duchy/kingdom revokation and with a significantly smaller vassal limit, to represent the increased breakdown of Roman order in Britannia.
The Germanic government, essentially representing the semi-Romanized government of the Merovingians, is similar to the Sub-Roman governments, but with a few main differences. Unlike the Sub-Roman governments, who mostly use Primogeniture or Feudal Elective, Germanic realms are locked into Gavelkind, as the Merovingians and later Carolignians famously exemplified in all its glory. Germanic rulers can also take concubines, to represent the Merovingian tendency to take multiple wives - even after Christianization - and hopefully produce more sons to split the kingdom between.