If you design a f2p game the formula MAU*Conversion *ARPPU will define your designers live. Whats important is that MAU is also a function of your setting & genre.
In other words if you pick a niche setting your reach will suffer, so will your revenue. If your setting is niche then marketing will have a harder time finding users - which raises acquisition costs which lessens your revenue.
So it is important to know how large your audience can be depending on those two factors. Hardly any marketing research has been done, most picks for those are gut feelings of the developers. Is science fiction niche compared to general topics? Or Fantasy?
If you look back into history you will notice that Fantasy on a world wide level was niche until Lord of the Rings hit the Hollywood blockbuster list. Yes, it was apart from one territory, the USA.
Oh no, you will claim, I read Fantasy all my life! It can't be! Well it was as you aren't the large reach audience, you are the niche. If you are large enough then f2p will work easier for you.
That is the difference between Clash of Clans and its "predecessors" Edgeworld (SciFi). Or why Candy Crush has such a large audience. Or why Call of Duty works better than SciFi shooters.
That is also why IP's seems to make it easier as there is already a defined audience. Note I say "seem" as that IP can also be a bane to your growth if said IP isn't popular enough.
So in order to lessen the risk, increasing revenue and lowering costs of user acquisition you should make sure your setting is cool - worldwide.
And I haven't even touched genre yet ...