From memory it was the need to do the necessary approval work to get something like an airline business class "pod" certified as being safe and what configuration would be safe. I think there was some concern that if you were laying in the direction of travel neck injuries would occur in a collision whilst in lay flat mode, obviously not a concern on an airline as the seat is in the upright position for take off/landing and if there was an emergency in flight severe enough for the position of the seat to be a concern it is likely to have fatal consequences anyway (otherwise there would be enough time to return it to the upright position)...there was something about crash worthiness the last time it was raised.
The approvals therefore were not impossible but the cost and delay of doing the necessary approvals was prohibitive to getting the stock in service on time.
Whilst I believe this simply because no-one can be pestered with doing anything other than the bare minimum (read cheapest and easiest)...Same argument as to why it is apparently necessary to have the lighting ambience of the custody suite at Greenock police station.