It may appear in this year. I was told it is in Japan already.
If you want to get "future proof" product, you will alway be waiting. After dual layer burnr, then there will be Blue Laser DVD which hold over 20GB and Sony is producing them now.
Get a 8x sigle layer DVD (e.g. NEC ND-2500) for £60 click here and more blank discs, and when dual layer come out with good price, get another one.