So here is the growing Python Hybrid list:
P.regius x P.anchietae -> viable cross
P.regius x P. curtus or breitensteini or brongersmai (all?) -> viable cross
P.reticulatus x P.molurus bivittatus -> viable cross
P.molurus bivittatus x P.sebae -> viable cross, albinism compatible!
P.regius x Aspidites ramsayi -> viable cross (NERD 2006)
Morelia spilota x Aspidites ramsayi -> viable cross (NERD 2006)
Morelia spilota cheynei x Liasis mackloti mackloti -> viable cross (NERD 2006)
Morelia spilota cheynei x Morelia viridis
So I guess the question of L. mackloti x P. regius is still up in the air!