A small dev diary detailing some changes that will be coming in the future:
One somewhat ahistorical but necessary change I'm going to be adding is a strait between the Red Sea and the Mediterranean. A kind of early version of the Suez canal connecting the Nile to the Red Sea operated until it was closed by the Abbasids and covered over, and not being able to transfer ships from the Indian Ocean to the Mediterranean is a problem. Ships could easily be disassembled at Sinai and reassembled on the Nile, and it will allow the Abbasid vassal fleets to operate in the Mediterranean.
The Byzantine theme system is also going to be overhauled. It will now alter the structure of your levies so that defence is prioritised over offense. You'll gain a lot of pikemen and skirmishers, some heavy infantry and light cavalry, but only a small amount of heavy cavalry and horse archers, which will represent the bodyguard of the local doux. The theme laws will be tied into a series of laws that will control the composition of your military, and will have two historical options, representing the theme system and the pronoia system. The pronoia system will active in later start dates, and will work in a similar fashion to the current theme laws, granting bonuses or penalties towards levy numbers. In contrast to the theme system, the pronoia system will be offensive rather than defensive, and will grant a lot of heavy cavalry and light cavalry, some heavy infantry and pikemen, but only a very small amount of horse archers or skirmishers, as the pronoia typically did not use bows.