That may be sound thinking as it introduces another way to exclude people paying to improve their pension entitlement (who live outside the UK and who may only have tenuous links with the UK).I think people applying to move from Class 2 to Class 3 might be regarded as "New applications to pay voluntary Class 3"
In practical terms someone with say five years record of paying NI in the UK, who then left the UK and was able to subsequently add to their record at class 2 rates for say 3 years, may now be excluded from buying any additional years at any price.