Well, I'm assuming old 4 will become "12" up to Hellroaring Peak. You won't be able to lap Connie's (probably a good thing, look what 5 did to East Rim -- destroyed it.), but you'll lap Hellroaring Peak and alternate from one side of the Basin to another.
Intermediates will have to use 1 to get to the back, but with Inspo and Hogans they won't be stranded. I'm more than happy with less pressure on the back. My daughter is severely unhappy with Area 51 being trashed, but truth be told, almost no one was skiing those acres.