The Google Pixel represents a golden opportunity... for Microsoft. By putting itself into direct competition with its own OEM partners and reducing the level of support it offers in stock Android, Google has created an Android phone with an experience that Samsung, LG, Sony and Huawei won't be able to replicate.
Microsoft has an extensive Android offering, in fact its Android software stack is at least as good as Google's. Meaning that a forked version of AOSP fully populated with Microsoft's applications and services would be a much more pallateable offering for those Android OEMs. Better than Google Play Services. Better than Windows 10 Mobile.
Perhaps the only sticking point might be the absence of the Google Play Store. To remedy that Microsoft could either approach publishers and sweet talk them into the Microsoft Android Store, or partner with Amazon, which has already done the spade work, and have a ready made solution.
For some of these OEMs Microsoft already has an agreement in place to pre-load Office Mobile and Microsoft's cloud services, so moving to a full Microsoft Android stack shouldn't be a shock to the system. Especially as all of these manufacturers are already Microsoft partners in other parts of the PC arena.
Microsoft may have failed with Windows 10 Mobile, but it isn't necessarily out of the mobile fight just yet.