I don't think anything is going to be made obsolete. I think we just have more options.
There are a lot of factors to consider when choosing a knife steel such as abrasion resistance for edge retention, toughness for stability, corrosion resistance, how often the knife will be used, ease of sharpening, and let's not forget price.
Buck knives didn't become obsolete overnight. Their 420hc blades are still selling well. There's a lot of different needs in this market. There's room for all kinds of knives and steels.
Having said that, I'm not a huge fan of m390.
I love cpm cruwear, M4, and magnacut. They're my favorite steels.
The biggest thing I've noticed is magnacut has such a good balance of properties. I love the edge stability and toughness. What I think really pushes it over the top for me is how it sharpens. I can get a screaming sharp edge easily and it doesn't chip like some other steels.
The biggest downside that I see is that a lot of makers run it too soft. Really, they're just not getting the best performance out of that steel.