Paternalism and its derivatives are well established technical terms of political/social/legal philosophy. People who use them in debates rarely think about their etymology; the gender-specificity of their origins normally plays no role in their choosing to use them. One uses these terms because one intends to defend some position on the issues that have already been framed by using these terms, in the extensive existing literature on that topic. That can be accomplished much more effectively if one uses the already established terminology.
There is no established synonym for paternalism in the literature. Of course, if one feels very strongly that paternalism should be avoided because of its gender-specificity, one can invent some new term, such as parentalism. However, if one wishes for one's arguments about 'parentalism' to be understood as contributions to the existing debates, one would need to say explicitly something like 'by parentalism I mean what other people mean by paternalism'. Chances are, though, that even with such an explanation, one would be imposing on one's readers the burden of 'translating' the newly introduced term as the old term they know, and that this would distract them from appreciating whatever argument one is otherwise trying to make. If one insisted on using such a term, one would be sacrificing the clarity and the impact of one's substantive contribution to the debate, for the sake of promoting a terminological innovation.
Incidentally, it should be noted that the origins of the term paternalism are tied not simply to the role of fathers (as opposed to mothers) in childraising, but specifically to their role in certain traditional, authoritarian methods of bringing up children. There would be something incongruous about creating a new, gender-neutral term for a concept that hearkens back to a different era.
