The current high kingdom system, while it will remain as is in 1.5, will be completely overhauled in the version after 1.5. This overhaul has already been done on the developer version but was not pushed into 1.5 due to insufficient testing. The new High Kingdom system will start off with petty kingdoms being permanently titular, unable to acquire de jure vassals, and will use vanilla mechanics in forming the high kingdom which means you will only need 66% of the HK's provinces in order to form it. Once you form the HK, your petty kingdom title will be destroyed. You will be able to own only one petty kingdom title and once you become a High King you will no longer have need for such petty titles.
This has the following advantages:
- In theory, the AI would be able to handle it better. In 1.4B and 1.5, AI kingdoms often broke up on succession due to having multiple Petty kingdom titles. This was also the primary reason the change was done.
- Far less maintenance scripts are required, which improves CPU performance. This means your game goes faster.
- The De Jure setup is now much more fluid. As a High Kingdom, you can now De Jure annex neighboring duchies using vanilla assimilation mechanics.
- It is now much simpler to create high kingdoms. Infact, there are no decisions to create high kingdoms anymore, they are entirely created through vanilla mechanics.
The downside is that this is such a huge change, that it will have unpredictable effects on the metagame. Considering this change was only finished yesterday, and we are planning to release this on Saturday, there is not enough time to properly test such a huge change, which is why it will not make it into 1.5 but rather the version after 1.5.
As for an Alessian bloodline trait, no, its not likely. The only lore I can come up with on the Alessian bloodline is that it is believed that Minotaurs, a hostile monster, are the descendants of Alessia and Morihaus. For all intents and purposes, that era is dead. The best you can do is resurrect the Reman dynasty, which starts off with fairly significant power in Colovian Estates.
Is it now possible to make the unit's look more like Imperial Legionnaires?
No, we cannot edit unit models at all, due to Paradox using a propietary format for their models.