Oh look, another Skyrim kid begging for dragons...

Ummm...I don't know how to tell you thi people, but the last known dragons lore-wise before Skyrim were during the reign of Tiber Septim, which takes place AFTER the events of ESO. Therefore, while having one ass a mount is rather farfetched, having at least one simply EXIST somewhere in ESO actually seems plausible. Provided the location is remote enough. Paarthurnax and Nafaalilargus are obviously both alive at this time (even though I doubt that we'll we'll see Paarthurnax in ESO XD), so other dragons are likely to still be alive at this point in the timeline. They're simply in hiding. It wasn't until Tiber Septim offered protection to the remaining dragons did they start coming out from those hiding places.