I would not worry so much about the motherboard and instead use an add-on RAID card. This way if the motherboard dies, you can still pop the RAID card into another machine to access the data. If you are using the motherboards built-in RAID and it dies, then you have a lot of potential work trying to find a motherboard that will read the RAID set as-is. Chipsets on RAID cards are often more "stable" in regards to longevity in use.
With the Intel Matrix Raid (ICHxR), you can easily move the raid to any other Intel motherboard as long as it also has an ICHxR chipset. However I'd simply buy a NAS and be done with it.