I feel if MS wants to follow Apple they need to create an ecosystem of products. Without a phone, this could be difficult. They should have continued to work on it until it was perfected. With control of Windows 10, they could keep inventing some synergistic features using familiar UI elements of Windows.
You're right though. With a history of failure, who wants to invest in a MS product only to have them abandon it a few years later.
In my opinion, the Surface has been their best invention to date. I love the idea of having one device that does (almost) everything running regular apps instead of simplified versions. Rather than having several devices (Apple), you can have one device which is excellent value to the consumer albeit less sales for the seller (Apple). The iPad is slowly getting there, but still has a way to go to become a desktop replacement.
While the Surface can run regular apps, now Macs will be able to run iOS apps. They're kind of going the other way around. This could mean some sort of eventual OS convergence but in order to do so, a developer would simply create an iOS app and hope that the experience transitions to MacOS. It should be interesting to see how this all plays out.
As a gadget geek, I would love to see a phone that doubles as your personal computer. You could dock it to a keyboard, mouse, and monitor. I know there has been a few attempts at this but for this to work, the phone will have to run a full OS and not Android.