This is a lot of things that holy paladins and prot paladins can do, and you probably already have those.
I can basically guarantee this won’t happen. Ret could do all of this on Algalon too, but was never stacked for it. After your holy pal + prot pal, you basically don’t need more DSacs / aura mastery / BoPs, etc…
You naturally have enough paladins to cover all your paladin utility needs before you put a ret in your raid.
After people aren’t dying to mechanics, you just go for best DPS to minimize how long the fight goes. That’s why ret was generally sat on Algalon prior to the buffs. It was better to just kill the boss rather than have an extra backup DSac/BoP.
It largely is. Mana constraints are rare in the first place. You don’t need full coverage of replenishment on everyone. There’s a huge diminishing return on it after the first.
If the ret buffs were reverted, you’d bring 1 arcane. Their damage isn’t bad, fire is just better.
Sometimes. How many do you need?
2 is a hard cap, they don’t need 100% uptime.
How many of these do you realistically need? It’s not an more is always better deal.
All of these marginal gains are weighed against Ret’s DPS. If it isn’t good, none of them are worth bringing a ret for when already covered elsewhere and you gain a marginal benefit.
Ret was largely sat on Algalon, a fight that theoretically used ALL of the things you listed, and it wasn’t used, needed, or helpful because it wasn’t worth the loss in DPS to bring marginal defensive benefits to your raid.