First of all, it takes time and intense dedication to master the Thu'um. Thus, that alone would "weed out the p***ies" as they say, and keep it from ever becoming commonly used. In fact, not everyone was able to wield the Thu'um in the ancient days. It's use was limited only to the higher echelons of Nordic society.

Now, since the dragons have returned and Alduin has been defeated, there is no doubt in my mind that there will be ambitious men and women who would seek out the dragons for this knowledge (at a price of course). From there, a new Dragon Cult may arise, and the Nords may hearken back to the old days of Atmora.

T'is all speculation of course.

Thats already been well established. Thats why I put common in quotations, and there's an edit. It basically meant in relation to what we have now, which is none minus greybeards and you. Common usage also doesn't mean common mastery or even proficiency, which is probably what people are getting confused with.

edit: There's also nothing that says it was limited to higher echelons of their society.

Last time they used the thu'um commonly-

in morrowind, where they got their *** handed to them by the dunmer.

guy that uses the thu'um (not player) currently-

Ulfric Stormcloak, who (in MY own subjective, and probably according to many, flawed opinion) uses Talos as a fig leaf the way conquistadors used religion...

NO.

If it was nearly as powerful as in lore, they would have not lost.

So stop making things up.