are u sure?^^ i always thought madara got izunas eyes and izuna was without eyes after that.
Yeah, my explanation was a bit confusing at first. ^^
Yes, he died without eyes. Madara took Izunas eyes and got the eMS. However, if Izuna would have lived at that moment too, he could have obtained the eMS due to Madaras eyes. But as Itachi said it, there's no surety for anyone to obtain the new light, even with new eyes.
In short: Yes, it would have been possible for Izuna and Madara to gain the eternal light at the same time. That is the only answer I could declare, if I consider the databook and volume 42.