Login to View Prices

Also referred to as 'Trade Logins' a feature to be able to prevent prices from being displayed and the ability to add products to the cart be removed until a user was logged in. This would be beneficial for trade-only websites who only with to sell to registered clients. This has the potential to be quite complex, so my suggestion is:

Phase 1:
The feature provides the ability to:
Display products without prices unless logged in.
Display products without the ability to add to cart, unless logged in.
Prevent signups via Customer Login.

Phase 2:
Display products to different users/groups of users.
Display price of products to different users/groups of users.
Display products with the ability to add to cart to users/groups of users.
Ability to vet account signups at shop level.