No, I don't think it's too out-there to use. Although I'd bet my eyeteeth you'll get that reaction a lot, since many people seem to be hostile to unfamiliar names just because they are unfamiliar. That's not unreasonable, either. But I don't feel that way.
Oddly enough, I actually prefer Idonia. I guess because
Idony reminds me (in sound & structure only) of
Ivory and
Ebony. Although I like the thrifty, tidy ending with the Y.
Idonea is a little too unconventional spelling/pronunciation-wise, to me, and looks fanciful because of that. I think if I used it I would use Idonia, and call her
Idony. In case it looked too cute (not serious enough) on paperwork.
Idony has a great meaning - a lot like
Persephone, but without the questionable etymology that seems to freak some people out.
I'd use a soft, expansive sounding middle name.. hmm.
Idonia
Mara (nn
Idony all)
Idonia
VestaIdonia
CharisIdonia
NatashaIdonia
ShannonIdonia
SolIdonia
Pascale