I was about to comment that the correct plural form of nova is novae, but it looks like dictionaries say that both novae and novas are correct. The irregular case does seem to predominate according to google ngram viewer.
As far as I know, it’s always valid, and perhaps even preferable, to use the regular -s plural with any Latin loanword, after all they’re English words now even if borrowed from another language. Using the original Latin plural forms in casual contexts feels a bit pretentious, especially when it’s not even the correct form, like "octopi".
Or words like status, where the correct plural would be statūs, i.e. the same word but a long “u”.
It is often the case that as the regular case increases in frequency, it becomes accepted as an alternative. It seems that lexicologists these days are less likely than formerly to insist that the philological roots of a word are the only determinant of correct spelling.