It would be a cool idea if we can add mobs to these new end biomes via config. This would really help pack devs who want to add interesting fauna from other mods into these biomes

I don't know if this mod is capable of doing what you want but maybe see if it can help https://www.curseforge.com/minecraft/mc-mods/in-control

I tried using in control but it doesn't work too well. The mobs just spawn all over the end when you try and tell it to spawn a mob in a better end biome. Idk if its a bug with this mod, incontrol or neither,

Never tried that mod but it seems it should do what you need, try it and give feedback maybe! I am not sure when i will implement a way to control mob spawning within mod config