Out of the last 4 champions, none of them defended the title, other than Machida (conterviersially).
The title has been passed around almost as much as Ariany Celeste.
Can Shogun defend against Rashad? Who wins and how?
They have nine former champions on the roster currently. Tito, Couture, Belfort, Liddel, Rampage, Forrest, Rashad, Machida, and Shogun (everyone but Frank Shamrock). Belfort dropped a weight class, and Tito and Liddel aren't making a run any time soon. So that leaves six former champs with a real shot at the belt. Not to mention guys like Franklin, Bones, Bader, and Nogueira. That's a stacked fucking weight class, 205 is ridiculous right now! 
I know I didn't answer your question, sorry, I don't know.
Trends are for the NFL - not MMA.
It very well could end up being a cycle of guys who are bad match ups for each other. I think if Rashad manages to out wrestle Shogun and either sneak out a decision or catch him with a punch on the ground like he did with Forrest he will probably end up fighting the Forrest/Franklin winner or maybe even Bones/Bader winner and their are a few bad match ups in there for him as well.
Machida can always rattle off a few wins and make him self a force in the division again as well, same with Rampage.
Personally I see Rashad holding the belt at the end of the year. With a win over Shogun and then a defense over Franklin probably.