Lucky they had the “-e” available.
(I don’t suppose a language would exhaust all vowels by having five genders, but I could imagine a language were e.g. all “female” words are randomly assigned endings “-a”, “-e”, “-i”, and all “male” words are randomly assigned endings “-o”, “-u”, and there is no gender-neutral vowel left.)
Portuguese uses the same vowels terminations for genders, but our articles are a simple ‘a or ‘o’ (instead of ‘la’ ‘lo’) and we also use ‘e’ as the and connector.
It means that the vowels ‘i’ and ‘u’ would still free for the third gender, but we do some vocal accommodation orally (I’m not sure about the correct linguist term) and often the sound ‘e’ becomes ‘i’ and ‘o’ becomes ‘u’ (it does not happen the other way).
Because of that, all of our vowels are already “taken” with just two genders.
I found it fascinating that it works so well in Spanish and not at all in Portuguese, even with both languages being very similar (I feel that Portuguese is slightly more gendered than Spanish).