1)This DLC plus its supposed included new (combat?) gameplay mode + the upcoming patch features (Golden Nug 'NG+', Wardrobe, maybe more?) may practically add up to an 'expansion', even if it shows itself to be a relatively 'smaller' one (while still bigger than any other DLC; like Citadel DLC was).
2)Three DLC was predictable. I would have wanted 4-5 (because where the hell is Sandal?, and I'd have liked a deeper exploration of the Green Fade and Demon stuff but it seems that's a no if the trailer is totally representative?), but 3 was very likely to happen.
As far as we know, there will be a Dragon Age 4. We can hope it'll take longer than DA2 to make (1-2 years), but it'll possibly not take as long as DAI (3-4 years), so I predict around 2017 (since 2016 is Mass Effect), unless NewIP alters that. But yes, at worst case, DAI 'underperforms' (big emphasis on the ''s) and this is the end of Dragon Age as we have generally known it. Ew. For all we know, the eluvians could end up the fast travel ports for a MMORPG. Ew. But we shouldn't assume this at all yet.