I assume there will be grandfather rights?
What gives you that idea? I haven't heard that EASA are planning any grandfather rights for the NPPL other than crediting the PIC flight time i.a.w. FCL.110.A(d) (i.e. you will still have to do at least 7.5 hours of dual instruction and 6 hours of supervised solo to get a LAPL(A)).
BEagle may have heard something(?)