I would try to hold onto a little bit of Bitcoins just incase something happens with the price or Bitcoin Unlimited doesn't go through.
This type Bitcoin forking and changing into something else has been happening year after year so I wouldn't be too worried about it. It just seems like there is just big money holders trying to cheat people of their Bitcoins when they cash out.

I would suggest that you exchange the coins only if you see any progress on Bitcoin Unlimited.