Naruto Chapter 446

[Yukimura]

Disclaimer: I am just trying to clear up a potential misconception I percieved.

A bloodline limit consists of multiple elements, but that does not mean that multiple elements is automatically a bloodline limit. In order for one to have a bloodline limit, it would have to be in his, well... bloodline.

Not really sure how to make that any clearer; that seems pretty cut and dry to me.

I believe you could make this clearer by not using ambiguous wording. Your use of "A bloodline limit" could easily be interpreted as "Any bloodline limit" which, in the first use of the phrase, could lead to a seemingly false conclusion, based on other evidence in the manga. I believe the Sharingan, Byakugan, and Kimimaro's bone ability are all acknowledged as BLs. These abilities demonstrate that not all BLs necessarily involve the blending of two types of elemental chakra into a new type of chakra. As you have pointed out it was also stated that the ability to blend elemental chakra into a new type is something that is only possible via a BL. If you take these two facts together and try to derive a theory on what a Bloodline Limit is from both of them you might come up with something like this: "A Bloodline Limit is an ability or attribute that someone not born with the inherent potential for can not 'learn' through mere practice or study or training."

This theoretical definition would support both unique physical abilities (seeing chakra, hyper perception, 360 degree vision, manipulating your bone growth rate, etc) and unique chakra manipulation abilities (Ice, Wood, etc) as BL's. It should also allow for something like Kakashi's seemingly contradictory possession of a Bloodline Limit despite not being of the proper bloodline. Taking into account that the Sharingan's abilities are properties of the eyes themselves (since Kakashi can use them) then one might theorize that the actual BL of the Uchiha clan is the ability of their bodies to develop (and perhaps efficiently support the use of) the Sharingan. In the same way Kimimaro's BL would be the ability for his body to manipulate and support the manipulation of his bones. As far as I can tell this theory doesn't contradict anything seen so far in the manga and more importantly doesn't seem to leave out anything that has been directly acknowledged as being a BL.

Other than that I am inclined to agree with Siddnne about the Rinnegan's omni-elemental usage not giving access to elemental blending abilities traditionally associated with bloodline limits. My impression is that a Rinnegan users chakra has an equal affinity for all six elemental types making mastery of any type no more difficult for them than anyone with a natural affinity for that element (possibly even easier than a normal person with an affinity). My personal theory about the Rinnegan in general is that the Rinnegan powers have nothing to do with the users eyes themselves unlike the Sharingan and Byakugan. I think the ring look is just a side effect of the true ability which is possessing a special kind of chakra with lots of abnormal properties. If you considering the way the multiple bodies were explained and the seemingly unique techniques attributed to the Rinnegan which have no obvious correlation with the actual eyes it seems to make a lot of sense.