Support for >2tb drives has been around since v5 beta 8.
They are in the final stages of a release candidate for v5 so the 'final' version is just around the corner.
Last week I upgraded my v4.7 to v5. It was quick and painless! Once I upgraded I replaced my parity drive with a 4tb and no problems there either. I then replaced one of my small 1TB drives with my old 2TB parity. Everything is running along smoothly.
I've got a mSATA SSD coming soon that I'm going to use for a cache drive. Very excited for the speed boost!