At the last meeting of the NPPLSC, it was decided that the target introduction date being worked towards is, if all goes well, 1 Jan 02; after that you should be able to start training towards the NPPL. However, there are many processes to go through before then, but all parties involved are doing their best.
The NPPL training requirement will consist of, inter alia, 32 hours of training and consolidation PLUS a Navigation Flight Test followed by a General Handling Flight Test. Due to the reduced number of hours required, ALL navigation training shall be carried out in the environment where the licence will be valid, i.e. the UK FIR, and the Navigation Test must be passed before the General Handling Test can be taken - those are the current proposals. So you might be able to do a few hours of GH in the USA at a PPL-farm, but NO navigation or Flight Tests. Which means it won't be worth the bother....