Marketing, and changing public perception is very hard to do. About 10+ years ago I was working in John Lewis, and the iPod was all the rage, but it wasn't the best music player available. Because of the popularity of the iPod, they had sold out.
You would tell people, we are sold out, but this (can't remember what it was) is better anyway! No, they want an iPod.
Now you don't get commission in JL, and you got no instructions to sell one thing over another, you were employed to know what you were talking about, so I was just trying to help someone get a music player in the run up to Christmas. But no, iPod or nothing.
As for multiple lenses when going mirrorless, I would think on average they would sell more than the one or two lenses sold with most DSLRs because a new system may have to totally replace a DSLR and multiple lenses. Apart from Sony mirrorless, I'm not sure you can use lenses from Canon, Nikon on other mirrorless brands reliably, if at all, via an adapter.
So if you go Fuji, Panasonic, Olympus etc, you are most likely replacing all previous lenses (if possible) when changing systems, and that may push the average up for 2+ lenses. Add to that that for Fuji, Panasonic, Olympus especially, the size / weight reductions of the system is also in the lenses, whereas you may have been able to comfortably carry a camera and a lens or two previously, you may now be able to carry a camera and 3-4 lenses for a similar weight and size taken up in a bag, so if size and weight was what was holding you back from buying more lenses, that may have been eliminated wit a change in system. Again, possibly adding to an increase in the multiple lens ownership numbers. And you would think a great incentive to get into a market when you will probably be selling more lenses with a new system.
I think I read that there is rumour of the Nikon mirrorless cameras only being available with a kit lens, at least initially, because it is a new mount, so no one will have other lenses for it. The availiability of adapters for older lenses is unknown atm. So straight from the off, if that is true, for every camera they will definitely sell one lens. What happens when someone buys multiple cameras though, time will tell.
I certainly would not like two of the same lens, especially with no
second hand market, because everyone has one.
Saying that, I don't think the Nikon mirrorless will be winning on size and weight reductions significantly. And I think that may be a good idea. Not everyone wants the tiny and light, though maybe a bit lighter.
DSLR users have been living with the size and weight to get the performance and ergonomics, the Nikon mirrorless may be smaller FF than their FF DSLR's, and any weight reductions compared to D5, D850 sized cameras with similar or better performance may be a big draw to many. They probably won't be smaller than the Sony's alpha series though, but for some that may be a good thing, and those people are what Nikon are hoping to attract. Depends if they are better or equal to Sony, or at least not too far behind.
Only days now until a lot of questions will be answered.
And a whole new set of questions arise.