Sorry, but one manufacturer can't take the entire OS to the next level overnight or over a year. Right now, majority of people are invested in apps and if Microsoft doesn't offer same apps on their platform, nobody will buy it. Another reason is that Microsoft themselves fail to advertise WP. When was the last time this guy went into a microsoft store? I go into a Microsoft store every week, and all I see is Surface all over the place. The phones are hidden somewhere in the corner where nobody can see them. Microsoft needs to pull their weight, and so far they haven't. The OS lacks simple things like orientation lock and different levels of brightness instead of 3 and many other features.
In 2 years, Nokia already increased marketshare of WP and in fact they were responsible for many new apps coming to WP that were already available on iOS and Android.
Unless Surface phone brings something absolutely insane to the table, it won't have a chance just like Surface itself. The reason why Surface Phone won't stand a chance without something truly unique is because the OS itself is the same on all phones. How will they differentiate? Camera? Not a chance. Design? Most likely not. Price? With 920 at $100, I don't think so.
In order for WP to take off, Microsoft needs to get more top devs onto platform and so far they haven't done it.
Let's do a simple test to see if Nokia changed anything. Who here joined WP for the first time because of Nokia?