I want a Vicky III however there is something I think should be pointed out and accepted:
The game will not be a big seller for PDS. It may be a success and turn an acceptable profit, but I would not expect it to rival the other big titles.
I say that not only to temper the community's expectations, but also as something of advice or a warning to PDS. If Paradox tries to broaden the appeal of a hypothetical VIcky III they will fail to do so, and instead the Vicky fanbase will be unhappy with the direction such a game took. Vicky II's economic model was very complex. I'd wager it required many programming hours to create and tune. It also turns off a sizable portion of potential consumers. But if they make Vicky III's economic model more "streamlined" and accessible, it still probably would not appeal to those who felt overwhelmed by Vicky II, but it would make the Vicky fans unhappy.
I suspect PDS is either aware of this or at some point had internal discussions concerning this.
I have my doubts about how much a vicky 3 would actually sell and be popular.. Most certainly less than HOI4 and Stellaris sold? It would be a catering to a very limited crowd who are already paradox fans but I think even most of paradoxians would probably not get it. So I have my doubts it would be a sustainable title (with the paradox dlc model in mind).
Just contemplative conjecture though.
There is no doubt in my mind that it would sell less than HOI4 and Stellaris. But as I alluded to above, that does not mean it could not be a success. Paradox can budget development with a specific sales goal in mind.
Should we expect the same amount of post release content as the other PDS titles? Probably not, but the game could still be sustainable.