Well I tried asking this in the metagames forum SQSA, but maybe more people will know the answer here.
Where can I find out about the history of OU? By that I mean not just bans from this gen, but the history of how it developed as a concept way back in the day.
Well you can search through the forums, but there isn't really a History of OU you should find quite a lot stuff about Gen 3 and 4, but before that competetive pokemon was so niche that it should be hard finding much about it in terms of History. During Gen 1 and 2 competetive Pokemon was mainly played with IRC bots, wich means it is text only and that doesn't really attracted a big userbase i don't know if there are still any members on Smogon that played during that day (especially since Smogon was founded after that days IIRC), but maybe you can find someone that can tell you something.
Gen 3 gave us Net Battle wich was the first real Pokemon simulator with Sprites and a decent Team Builder (there might be others at that time, but i only ever played Net Battle and never heard of another one) which attracted a lot more people and competetive Pokemon started to become more popular. Since you asked about OU in specific since the simulators didn't had any way to collect usage statistics back then the tiering was decided by a single person the BL tiers where also a lot bigger back than and BL actually was a real tier and not just a Ban List there also was no RU or NU since UU was rock bottom.
Gen 4 gave us Shoddy Battle wich later got to be Smogons first official Simulator and we started to base our tiers out of usage statistics and not just the opinion of a few select persons and the suspect system was introduced to determine possible Ubers and also added the NU tier wich despite being rather popular at the end of Gen 4 never was a official meta game like OU, Ubers and UU (and LC) oh and the BL tier was cut down to just be a Ban List rather than its own tier in the beginning of Gen 4 there was also a new simulator developed from Cathy just for Smogon however it never really took off in popularity especially since Pokeon Online had Gen 5 support faster.
When BW1 came around Smogon switched to PO as its official simulator for quite a while, the suspect test was a little different back then since every voter who qualified was allowed to put suspects to vote this was effective in the very early stages since it allowed us to ban a lot of broken Pokemon like Shaymin-S, Deoxys-A/N, Darkrai and Manaphy very fast wich were OU in the very begining of BW, but later on stuff like Latios, Dragonite, Volacrona and even Reuniclus were suspected and after round 5 of suspect testing we switched to the council system we currently have.
That was about when BW2 came out and we switched to Pkemon Showdown! as our official simulator and thats pretty much everything up until now that i know of.
However a lot of the things that happend before my registration date are just things i heard of. I am pretty sure there isn't too much wrong, but if there is feel free to correct me. I can't really give you a list of major tiershifts through the Generations if thats what you are looking for and i doubt that there is someone who remembers everything, but with a little searching through the forums you might find soemthing of interest.