Far fetched even when we have seen what Madara has done with his Susanoo, it being two headed and able to use PS. He also said that they have to be clansmen to work along with his not always gaining power statement. You seem to be ignoring some of the page and putting stuff out of context to hold onto your initial opinion.
"Many Sacrifices piled up over the course of
Our clans history."
He even initially stated that it is obvious that the exchange could only be dont between clansmen.
All the uchiha were aware that the exchange had do be done within the clan from patterning Madara and Izuna. Itachi was only emphasizing on this for Sasuke's sake (lack of knowledge).
Why would they replace their sharingan with some random eyes? It's never been stated anyway...neither was the implication ever given.
When you think about it it's not that far-fetched. They're a clan that loves power and will clearly stop at nothing to get it. I can believe that once they saw Madara and Izuna with MS, and Madara with EMS, that they would try everything to get it. They had to create Izanami to stop themselves from over-using Izanagi.
Your theory has no foundation. There was never an implication of uchiha's using random eyes as a means to get EMS.
Itachi even stated that it was obvious that the exchange would only work between clans men.