Yes, the date has been extended to June 1st, 2013.
Is there any way to purchase upgrades through the BFL website, or is there a different website for upgrades?
This. I'm looking to upgrade some units, but there doesn't seem to be an option for them anymore... Nice to know the deadline has been extended, but I want to get some orders in as soon as possible.
Go to purchase a BFL SC Single. On that page is a button to indicate that you're using a trade-in.
This is for buy one / trade in one, IIRC.
Might not be a convenient way to do multiples. I dunno. (Didn't need to know at the time.)
Have you seen their new website? They did away with the old system and tried to put in a fancy new system, which seems pretty cool, but it's got some issues still. There is currently no way to order an upgrade. It might be possible to put your order in, make a note and wait until someone gets you an updated price on the order before sending payment, but I'm not sure.