I started a new game at the Dec 25, 1066 start (my usual start), and have played almost a decade in. Anyhow, wanted to give a couple of quick observations:
- The Byzantines were actually winning the Seljuk-Byzantine war for the first year or so, reaching a warscore of ~30%. I found out that this was because the captain of the Varangian Guard was a 21 something martial leader with the mountainous terrain bonus, and most of the battles had been fought in the mountainous terrain of Armenia / eastern Anatolia (in the biggest battle ~10000 Seljuk troops get decimated by a mere 3000 or 4000 Byzantine troops). The captain however got killed and, of course, the AI being the AI, it all went downhill for the war. Not bad, though, since it shows the Byzantines do have a chance of success if they're lucky - but the chances of that happening would be rare.
- The Byzantines exploded into at least 4 civil wars within a couple of years of the end of the first Seljuk-Byzantine War, and crown authority is dropping fast. Though this is technically not a problem per se, it is historically implausible in the sense that as part of a much more centralized state, Byzantine nobles would be more likely to try to get another guy on the throne rather than turn Byzantine into a feudal state. Is there a way to increase the chances of Byzantine nobles preferring claimant factions over lowering authority factions? I think it would be a bit more historically plausbile. However while I haven't played much of this game I suppose it won't be much of a balance issue in the long run, more an issue of historical plausibility (that was already present in vanilla, anyways, as you know).
- On the other hand, it looks like the number of English claimants is down, which is nice. I would suggest giving Svend of Denmark a weak claim on England as opposed to a strong one - currently he has a strong one, and he has plenty of healthy heirs running around.
- Turning Shia into a heresy seems to have a minimal effect on the Fatimids' vassals' opinions of the Fatimid rulers, although I guess there isn't much that it could do given the heresy opinion penalty isn't that large. This is partially because it seems like the Fatimid liege was handing out landed titles left and right to a bunch of people (many Shia), raising their opinion of him. Thus, so far in my game the Fatimids are still one big happy blob, while the Seljuks (unsurprisingly) exploded into a massive independence faction revolt right after the Seljuk-Byzantine war ended. However, on the bright side, there were a few Fatimid vassals who absolutely hated the Fatimids because of the religious difference (among other things), so I think it's still a good change nevertheless.
- Oddly, the Shia ruler attempted to conquer Alexandria, held by the Coptic Pope. I think the war is still ongoing when I stopped playing for the night.
Overall though I think the changes are good, and as I said I've only played about ten years, so... yeah.
Also, as a side question, did you remove some of the Komi provinces? I noticed they were still there but unoccupied.