I do think each borrow will be worth more than the normal roughly $2, but I don't think it will be double, even though the fund has been doubled.
Remember, all new Kindle Fire owners get a free one-month trial of Prime, not to mention all the people who signed up for Prime on Black Friday so they would get free 2-day shipping for the entire month leading up to Christmas -- many of these people will cancel their Prime membership before the end of the 30-day trial period, but they will probably take advantage of their free borrow during the month they have it. So there are likely to be a lot of "new" Prime members during this month.
Not to mention the fact that the KOLL is now available in the other countries' stores (particularly Amazon UK)/
The increase in the fund reflects that Amazon expects to see a lot more borrows than normal. Yes, I do think the per-borrow rate will rise, but I certainly don't expect to see it at $4 or anything crazy like that. (Although it would be pretty awesome if that were the case.)