I'll be honest I am not really on board with the semantic arguments about how that death rattle 'could not' be talking about Ishar.
Language isn't perfect and especially in cases like this where Brandon was clearly going for a certain vibe, a poetic feel, a *rhythm* if you will, to the death rattles you have to accept at least a small amount of license.
In essence you could absolutely say that "the burdens of nine become mine" is functionally no different (albeit more ambiguous) that "the burdens, which had previously been split among nine including myself, have become mine".
I'm not saying it's 100% talking about Ishar or anything but I feel that claiming it *can't* be about Ishar is ...I guess proscriptive and pedantic in a way that doesn't mirror how language is actually used? Just my two cents on the matter.