I was tihnking maybe something like help protect seyda neen? Or perhaps gain your own fort once you've become an imperial knight?
http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=3122 is one that comes to mind, It even has an option to place the castle over in http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=3494 instead of the Bitter Coast. Ald-Vendras will also grant a castle to a master in the Fighter's Guild.
http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=461. Wear any armor like the http://home.comcast.net/~hdoan0/Knights_of_Tamriel.htm series or the http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=1061 (includes Knights of Tamriel).
I've never played it but the http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=904 mod involves the Imperial Legion.
I don't know, there's more out there. I just got these off of my outdated http://www.mwmythicmods.com/knight.htm.