A NPPL with SSEA Rating can indeed be upgraded to a JAR-FCL PPL(A) - it's all in LASORS!
Any instruction conducted for the NPPL by JAR-FCL FIs will be counted in full towards the mandatory requirements for the JAR-FCL PPL(A) - so it's basically a top up course.
If you have a NPPL and fly a long solo cross-country which meets the JAR-FCL PPL(A) requirements for the Q X-C and have the completed form to prove it that will also count.
There is no guarantee that the 'R'PPL being considered by EASA will be identical to the NPPL. But we aim to present an industry-agreed NPPL to them that has succeeded.