It is taking forever as they do not intend to upgrade ( if that the right phrase) all the aircraft. BA have taken a decision that they can fly around the old cabin until the new aircraft arrive. As the IFE is pretty dire on these old aircraft, they have been equipped with iPads in an attempt to gloss over the poor state of these cabins. ( all the while charging the same fares)
Consequently unless you are on certain routes there is no guarantee that you will get New First. There is a site which will allow you to rate your chances and the link is below.
I think this says much about BAs commitment to delivering a premium product as no business which genuinely wished to do so would allow such tat in the air.