The JP version of FFXIV already uses suffixes to denote strength.

English: Thunder, Thunder II, Thunder III, Thunder IV
Japanese: Thunder, Thundera, Thundaga, Thunderja

This is evident if you watch the Live Letter again and hear Yoshi talk about the new changes to spells and he says "Sunda, Sundara, Sundaga, Sundaja", referring to Thunder 1-4.