There was an attempt in John Ford's 1984 novel "The Final Reflection" to describe the Klingons as a multi-racial society, although the details escape me now. Vonda McIntyre also picked up on this concept of a multi-racial Klingon Empire, IIRC. I always assumed that the Klingon Empire was a kind of "Mirror, Mirror" reflection of the Federation, only in the Prime TREK Universe, complete with internal cultural and racial/species diversity. There never was any clear canon guidance on this, however.
In the 1980s, I interpreted the human-like Fu Manchu-style Klingons as being of a race/species that were more anti-Vulcan than the Romulans. Kor, Koloth and Kang struck me as being coldly logical and militaristic in stark contrast the the (relatively) warm and polite Vulcans. When the tire-tread-headed Klingons came on the scene, I recall one fanon publication (an Enterprise officer's manual?) describing an ethnic/factional takeover in the Empire; thus the "new" Klingons became prominently featured.
The Klingons of TNG seemed to be even more of a shift, keeping the same tire-tread prosthetic makeup (didn't Arsenio Hall once describe Worf as looking "like he has a butt on his head"?
) but further exaggerating the behavior until they started reminding me of an overdone caricature of General Urko from the old PLANET OF THE APES series from the 1970's. It never made sense to me that a race so immersed in violence, so conflicted from without and from within, could've made it into space without perishing in their own world wars.
That having been said, the ENT take on the Klingons nearly wiping themselves out with an augment mutation sounded like a lame plot device. I still think the Klingons make more sense if they are a multi-racial organization of worlds. The well-done Klingon costumes in TMP6 suggested to me that with a little effort the Fu Manchu-style TOS Klingons could conceptually make a comeback and not
look 1960's-TV cheesy.