@Mnementh
I highly doubt those indie games sold 1.5 million on Steam like D:OS. Larian isn't some simple 2-d platform studio.

I hear this all the time "due to portability" but not all games are really equally well suited for such.... this game isnt that type of game.

It's more than possible with a controller, it's damn near flawless on PS4 with the DS4. Perhaps it's the port for the Enhanced edition and maybe on PC controllers aren't as well supported, I'm not sure about the PC version but it's by far the best Aprg control wise with a controller. The only thing that beats it is Xcom and that's fully TBS focused and built with the controller in mind. 

I didn't say DOS was, they just did a fantastic job with it. And I specifically recall the devs of Enemy unknown saying they designed it so it would work with a controller just as well, regardless of whether they had it "solely" in mind they had it in mind and made game design decisions to optimize for controller and the game sold many more millions of copies because of it. Don't get in a fit I'm not getting back into the argument of this, we've done it twice before.

I very much doubt it would have sold nearly as much off of PC had they not had the forsight to do so and It probably wouldn't have made it on to mobile either if it was specifically optimized for k&m then updated after the fact.

Let me answer instead.

Answer to question 1: obviously no, I already own it for PC and still strongly consider double dipping for a great game and portability.

Answer to question 2: Dunno, but what does it matter... it matters how many are buying the game at all, regardless if they do buy it only for Switch or buying multiple copies for different systems and regardless if they own multiple systems. Larian couldn't care less about your question, they only care for overall sales.

Your question sounds like: How many PS4-only players would consider buying GTA? Or how many would buy GTA only for PS4 although they own more consoles? Obviously all that didn't matter, all the PS3-owners bought the game willingly again for PS4.

I'm not sure what you mean, exactly.  Redundancy is absolutely something businesses consider.  I'm pretty sure it's why some of the bigger publishers aren't that interested in developing the same audience on Nintendo platforms as on PS/Xbox/PC.  If a significant number of people would buy the same game on a different platform then there is less reason to spend time and money developing a port.  It's the remainder, the people who would only buy that game on that particular platform, that represent a gain.  

That's ridiculous. A sale is a sale. The businesses don't care and often even don't know which sales a for double dipping. I say it again: games like Tomb Raider, TLOU and GTAV had a lot of their sales on PS4 through double dipping from owners of these games on PS3. It was a big win for the publishers of these games. Same is happening now with Mario Kart and that's why Switch also gets Donkey Kong Tropical Freeze and Hyrule Warriors. Because these double dipping sales matter as much as first time sales.

You try to single out some sales and declare them irrelevant, as if they don't bring any money.

I honestly don't think you know what I'm talking about.  I never said double dipping sales are irrelevant.  You're the one that brought that subject up.  I specifically referenced people who own multiple platforms but would only buy a specific game if it came to one specific platform as opposed to people who would buy that game on platform A if it skipped platform B.  Neither of those scenarios represent double dipping at all.