I've just noticed that blank Blu-Ray discs are starting to drop in price.
A 5 pack of 2x speed Verbatim BD-R discs are now £32.99, which works out at £6.59 a disc. Still quite expensive, but half the price they were in December! So the price is falling.
Maybe by the summer BD-R will be an affordable large media format. I will definitely be buying a Blu-Ray writer as soon as the discs are affordable. 25-50GB per disc will greatly improve the manageability of large rom sets.