RK47
collides like two planets pulled by gravity
Personally I think in HRE they should finally create an all-new set of mechanics for it (it needs to be much more loose, so it doesn't end up solely composed of Germans and as the grand central blob). And while at it, do something about the way Karlings keep surviving.
I am going to disagree. What the HRE needs isn't special mechanics to make it more loose (after all for parts of the period it was much more coherent, and things could have gone differently, leading to a much more powerful and central monarch there), what is needed is a massive change to crown authority. It shouldn't just be low/med/high, it should be lots of little laws that add up to being those and it should be difficult to move up the ladder, especially in multicultural kingdoms/empires.
The Karlings are a problem though (mostly just because they gangbang everyone who tries to supplant them in TOG start). No idea what to do there.
Actually having Low Crown Authority isn't a big of a deal from what I've experienced anyway.
It's holdings that lets you climb up from the low rank. Keeping your prime duchy well-developed and stocked with gold and army is key factor in getting that crown.
Then once you get up there - don't take more counties for yourself, instead spread out the power between count vassals, while expanding your demesne by strictly building more castles in your capital county. A 4-castle capital is strong as hell when backed up with a 20 martial marshal and retinues.
As for Karlings. They hardly work together maybe an alliance here and there - but they warred each other too. I played as Count of Nassau and took out Germany from a Karling, from then on, I just backed every revolt against a Karling kingdom with my army. Eventually Italy is ruled by an italian and Aquitane went their own way, Bavaria gets swallowed by Hungary (Karling vs Tengris lol) and the remaining Karlings only held on to a mess of France and western Europe.