Haha, you read my mind on the note of adding a cast time. A few hours ago I was like, "Hmm, what if they had a stance that added cast time or more of a 'draw bow' time." But then, like you said, the Bloodletter mechanic would need altering because even with less mobility but higher damage it'd play just like BRD. If a stance was used that did this though it would have to be attractive enough to maintain it else people just wouldn't use it and would again just be playing like BRD but with new mechanics. My exact idea on adding cast times was to create a system where you would press the button once and it would start filling up a bar. You can press the button again to shoot the arrow at any time with no animation locking but the more you let it fill up (ie draw your bow tighter) it would deal more damage. You could still move while it filled up to dodge fight mechanics but it would drain the bar the longer you moved. I'm planning on changing Aim into the stance.
The idea for positional requirements stemmed from hunting. Gaining certain vantage points and getting benefits from them. But perhaps overall it's not that good of idea. Probably better suited for a Ninja type class to teleport in and out of melee range whatnot to make use of positional requirements.
I forgot the lore differences in Elezen and ancient Miqo'te archery. Would be neat to do something with this but I don't think I could make it work well. BRD's relic weapon is essentially a longbow but focuses on fast movements and all that. So then Ranger would have to focus on slow/tactical movements but with a shortbow. Just doesn't sound right to me.