It was said during the undead reveal stream that 48 Skill crafting skills are available so yeah 24 regular and 24 Source skills would be my bet too.
Now Tyranny, I was hyped by the game for this spell crafting but in the end I felt that it wasn't that great and I prefer that Larian added "Hidden skills" (you do use crafting system but you don't really craft them as in choosing their effect) rather than having some mildly interesting system with 200+ possibilities but only a couple are interesting.
I still think the spell crafting of Morrowind was fun (was a long time ago, maybe I am just nostalgic) and I wish it would be made again and improved in a different game.
