Overall coir is regarded to have a good balance between air holding and water holding. It can be very high in K potassium, so it may be easier to source an amended product, with added Ca and Mg and or other trace elements or pH balanced to a desired range. Coir comes in various grades, fine to coarse, so not all at either end would be suitable for Citrus seeds.
Coir is now used in vegetable seedling punnets and plugs, for lettuce etc. These plants have fibrous shallow roots. Citrus seedlings develop via taproots, and this root can be well down into a pot, with not as much showing on top.
In any pot medium, the height of the pot is very important. In the case of Citrus, the taproot will be well into the saturated zone in a shallow pot, compared to what would happen in a tall pot with the exact same medium. In a tall pot the saturated zone will be lower down, and the air holding balance will actually increase.
Apart from air holding and water holding, you probably need to consider the rate of the media surface drying. This could depend on temperature, season, use of grow lights etc.
You could do some trials with supermarket lemon seeds etc, before you commit any more valuable seeds.