Microsoft had already released Windows 10 Mobile to eligible Windows Phones on 17th March. Microsoft has now also confirmed that they are allowing users to make a choice between the two different kinds of Windows Phone versions. Even though the new OS Windows 10 mobile is an upgrade to Windows Phone 8.1 but it was actually started from scratch in terms of coding and all that. Officially released OS is still having some issues with some users. Therefore, users can go back to 8.1 and wait for Windows 10 mobile Platforms to get matured in upcoming updates and then get your smartphone upgraded to Windows 10 mobile.
@GabeAul For a Retail user going from 8.1 to 10 who may hit an issue and need to recover, they need an 8.1 image to recover to.
— Jason (@NorthFaceHiker) April 4, 2016
@zayn_brandon @neil_hedley @windowsinsider @GabeAul No plans for that. Devices that originally had 8.1 will keep those orig recovery images
— Jason (@NorthFaceHiker) April 4, 2016