No one knows for sure but the Xoom is probably the most likely first generation Honeycomb tablet to get upgraded to Ice Cream Sandwich.
As for other phones and tablets its anyone's guess. It's up to the manufacturer and we all know how long one can wait until an upgrade comes through if you get one at all. My advice is that if you don't like the OS the hardware is running currently that don't buy it based on a promise or an assumption. As we know from the Xoom, manufactures often make ridiculous promises that they can't keep later.