We need to remember that prior to EASA (lessor extent with the JAA) we had 'need to know' but clearly defined paths from the various NPPLs and also from Silver 'C' and Bronze gliding certificates to PPL. There are a number of modifications required to these various courses to update them but previously ICAO had not raised any issues with these to my knowledge. The short courses ensured that the ICAO requirements were completed.
I regularly taught and examined glider pilots and the NPPL range of licence conversions with few problems. The EASA barriers are artificial. The CAA then have good templates for all this and together with AOPA should be able to move quickly.