In the past, reading the Song of Pelinal, I had noticed the following section, and wondered about the 'mechanics' of it:

"O Aka, for our shared madness I do this! I watch you watching me watching back! Umaril dares call us out, for that is how we made him!" [And it was during] these fits of anger and nonsense that Pelinal would fall into the Madness, where whole swaths of lands were devoured in divine rampage to become Void." - Song of Pelinal, Volume 6

There is, then, the matter of the following quote, born with the knowledge that Talos = Ysmir, the "Dragon of the North" (or a portion of the Enantiomorph).

"Also during the Late Merethic Era the legendary immortal hero, warrior, sorceror, and king variously known as Pelinal Whitestrake, Harrald Hairy Breeks, Ysmir, Hans the Fox, etc., wandered Tamriel, gathering armies, conquering lands, ruling, then abandoning his kingdoms to wander again." - Before the Ages of Man

We also know that Wulf/Wulfharth utilized the Thu'um:

"The second song of King Wulfharth glorifies his deeds in the eyes of the Old Gods. He fights the eastern Orcs and shouts their chief into Hell." - The Five Songs of King Wulfharth

Finally, Pelinal's proclivity for laying waste to entire swaths of land reminds me of the following:

"Soon the Greybeards made known that they were restless. Already the storms had begun from their murmurs. The Greybeards were going to Speak. The surrounding villages were abandoned as the people fled the coming blast. The villagers warned Talos to turn back, for he was marching to the mountain where the Greybeards dwelt." - The Song of Tiber Septim, Pocket Guide to the Empire

We connect the dots. So the question is this: Todd Howard confirms Talos as one, but was Pelinal (or the Pelinal incarnation variant), himself, a "Dragonborn" in the sense of the protagonist of Skyrim, and did he possess the Thu'um, or Voice? I am leaving all Shezarrine-esque questions aside for the time being.

The term is just too uncertainly defined right now to say, I think.

By the way, the first thing that came to my mind upon "[And it was during] these fits of anger and nonsense that Pelinal would fall into the Madness, where whole swaths of lands were devoured in divine rampage to become Void." - Song of Pelinal, Volume 6" was Alduin World-Eater.

Pelinal was the avatar of Shezarr and the god of time, wrapped into one nice package.

If you ask me, calling EVERYONE who did something significant a dragonborn is diluting the term heavily and making it too broad.

The phenomenon of your character absorbing Time-Eater dragon souls, and Shezarr's mix-up with Akatosh during the Alessia amulet handoff, plus the whole "[Let us] now take you Up. We will [show] our true faces... [which eat] one another in amnesia each Age" make me think this link is somewhat automatic. A bit of a Sharmat/Hortator 1-and-1 ruling king thing. Which is reminiscent of the line "A ruling king that sees in another his equivalent rules nothing", which may hint at the conflict in Skyrim.

But yes, probably the easiest summary is that it is way too early to tell.

Actually, the key question quite possibly ends up being whether the Ysmir referred to in "Before the Ages of Man" (Pelinal, Hans the Fox) is the exact same in identity as the Ysmir, Dragon of the North, Talos. Or if they are simply both so named. Or both avatars. Or somesuch.