Really the 8GB RAM as an option would be the only thing that would make me just keep my 2011 model another year. The main reason I wanted to upgrade this year so soon was to get 256GB SSD and newer processors, but 4GB is so small and I am always paging out to the drive to the point I end up with 8GB swap being used just from having a web browser open. (Flash. It's FLASH DOING IT GOSHDARNIT!) I had 8GB on my old Pro and never had those problems. So I'm crossing my fingers we get an 8GB option.
512GB SSD wouldn't matter to me since it'd probably be extremely expensive. I only want 256GB just to give me room for Virtual Machines, a Windows partition and all my Steam games.
And USB 3.0 would be as useless to me as Thunderbolt. I don't own any products that use them and if I did, I wouldn't be using them on my Air. They'd be used on my Mac mini, which I'd have to replace, if I wanted to spend hundreds and thousands replacing the 15TB I already have connected via USB2.0.
3G/4G would only matter in a world where cellular companies weren't so greedy and instead offered an ala carte option for a single user to use up to 2-3 devices on one 3G/4G data connection. I'd use my iPhone, buy a Cellular iPad and a MacBook Air with Cellular if I could use each one at will without having to pay separately for each device. It makes no sense and I would end up never using each device enough to justify separate prices. So there should be a single pool option that I could connect individual devices to that would drink from the same "data" pool. THEN I'd consider cellular on my non-phone devices.
And Retina, well, I'd LOVE it, but am willing to let it come in time. I do hope the rumors are true, but won't be devastated if they aren't.