The impression I've gotten with Windows 10 (including mobile), is that it's essentially a "long con," for lack of a better name. The initial versions of mobile aren't necessarily supposed to save the platform, but it's supposed to be the building blocks towards creating an ecosystem with almost no barriers. You have desktop, mobile, hololens, IoT, Band, tablets, etc. Mobile is a major part of that, but it seems like they know that they aren't ready to give that next big mobile push. Despite how much I hate people saying it, W10 Mobile (I don't consider the PC this at all), is still in "beta."
That's not to say it's unusable by any means or even incomplete, it's just very early and is being fine tuned. I also believe that once it hit 10586, it was incredibly stable. The difference I saw between some of the earlier builds, and that build in particular was monumental.
What I mean by that is that this is how they are getting W10M ready for the big time, which would be the Surface/Panos Phone. I've been using it as my daily driver since about Thanksgiving and I've had no major issues with it. It may not have all the bells and whistles that everyone hoped for, but it does the job. It's just as stable as most of my Android phones ever were, if not more.
All that said, Windows 10 (including mobile), is a very long term idea from Microsoft. It's about breaking down the barriers between devices and adapting to devices and form factors. Without Mobile, it fails. While I don't know what Microsoft is thinking, I'm sure they know what they are doing. The Surface line 4 years ago looked to be a total disaster, but look at it now. If Microsoft can garner even 30% of the success of the Surface if/when it is applied to mobile, they will have succeeded. Keep in mind, that the success the Surface line has generated so far has absolutely changed the definition of laptops and tablets. Both Google and Apple released their own versions of the Surface this year (neither with anywhere near similar capabilities), and it has inspired an entire new product line of 2-in-1's and transformed laptops and tablets with Windows 8/8.1/10.
The whole idea of One Windows (or whatever this strategy was called) has been in the works for years, and this is only the beginning of the unity we're seeing of the platforms. This will continue to change and grow going forward, and it truly is something that will take a long time to fully manifest. The general unity between all the devices seen already is a very welcome start in my opinion.
Personally, I think Microsoft has the right idea here, they've thinking long term and I wouldn't bet against them with how well the Surface line has done to move the entire marketplace. Additionally, given the traction Windows 10 for PC has gained, that likely will have at least some positive effect on Mobile as well, even if it takes some time to manifest.
TL

R; This is a long term plan, desktop might be able to carry mobile, and using similar techniques as were used with the Surface line could still save Windows 10 and Windows 10 Mobile.