I've just applied for this and have just received this reply:
"Dear Sir/Madam,
Thank you for your application for an AFPEx account. The system is now in operation and we are concentrating on migrating aerodromes and companies who are currently on legacy systems, which are due to cease. The timescale for GA pilots going onto the system is expected to be in early May. Please be assured that we will handle your application on a strictly "first come first served" basis and you will be contacted in due course. Your patience is appreciated
Kind regards,
NATS AFPEx Team"
In the meantime, I'll carry on using the superb French system, OLIVIA - which has so far worked pretty flawlessly for me over the last 2 years.