If K390 is cheaper, then sure. But isn't Maxamet USA made and K390 European, so it's harder/more expensive to get K390 into USA models? I thought that was why we see the Maxamet Native or Manix (golden) but the K390 Urban or Pingo (Maniago).
If the Manix2 LW was available in K390 I'd probably buy one for novelty, but my use of the two steels (the Manix LW Maxamet is my most common EDC, and the Urban K390 is my most common travel EDC) has left me with only a very slight preference between them, and I already feel like the Maxamet models are a fantastic value, so unless there was a major cost savings, I doubt it would matter to me. And I think the market for these kind of carbon uber-steels is pretty much limited to knife people (non-knife people always opt for stainless options, and probably ought to be guided toward them regardless), so my guess is that price difference wouldn't make a huge difference to the average k390/Maxamet buyer, unless it was a pretty large price difference.
And I agree on the toughness. That matters to me for larger blades (even smallish ones--I have a k390 PW custom that I wouldn't trade for Maxamet) but in the smaller sizes I prefer edge holding to toughness. Which is another good argument for K390 in the Police, but not in the Native.
Hmmm....thinking about that, I'd be most interested in K390 in the larger Golden models--like the Military and Manix XL. I bet a K390 Military would fly off the shelves, and I'd definitely buy a K390 backlock Manix XL, although I might be a small niche buyer there.