HP's Windows 10 Mobile-powered Elite X3 didn't do well in the market for a number of reasons, and rumor has it that HP is looking to fix at least one of the things that made the phone unpopular by making a sequel to it that runs on Android. The premium handset was marketed mainly to the enterprise segment, and its main draw was Microsoft's Continuum functionality which allowed it to run a full desktop interface when docked. An Android sequel would likely fall along the same lines, though manufacturers have always had some difficulty providing such a solution due to Android's mobile-first design and underpinnings.
It doesn't take a market analyst to tell that Windows 10 Mobile is all but finished at this point, at least in its current form. Microsoft reportedly plans to ship a final update, dubbed Feature_2, which could be supported as far out as the end of 2018. This will mark the end of the current iteration of Windows 10 Mobile, and whatever Microsoft chooses will likely stick to newer hardware. If all of this is true, it essentially means that Microsoft is either planning to create an entirely new mobile ecosystem or is going to go with an established mobile OS such as Android, pulling out of the ecosystem game altogether, and simply promote its software and services on that platform.
As for the HP Elite X3 and its rumored sequel, the fact that the Qualcomm Snapdragon 835 can emulate x86 instructions fairly well may end up being a deciding factor in how a new device is approached from the design standpoint. Given the current state of relevant technologies, making a phone that runs Android on its own screen and boots up full-on Windows 10 when docked is entirely feasible, and may just be the direction that HP takes with its next smartphone. There has also been mention of Microsoft working on something called "Andromeda OS", a name that's already taken by a project within Google's wheelhouse, which means that there could be some overlap, quite possibly with the Snapdragon 835 and future chips like it at the center of the whole thing.