Asus Transformer Prime should last about 15 hours with the keyboard dock. It's based on ARM. I have no idea if Vim can work on Android, though. Maybe this will work:

https://market.android.com/details?id=com.aor.droidedit&....

https://market.android.com/details?id=com.touchqode.editor&#...

There are others, too. If you need it right now, this is the only one that can last that much. But if you're not in a hurry, you might want to wait for a larger screen combination, which I think will appear by summer or so.

Here it is, even lighter and half the price of a Macbook Air:

http://eee.asus.com/en/eeepad/transformer-prime/specificatio...