Good new ! for Moto E 1st gen user They can soon Download Android M Rom for Moto E 1st gen 2014 but you have to wait for some time because the Rom was Ported by an Xda developer Lukeiss_dunne on his thread on XDA and his team and they have already started the development of Android M for Moto E and Hope So it will successful so that we can get Stock Android M 5.2 for Moto E 1st gen 2014 Soon.
This port will be 100% stock Android and will not be changed/ customized.
When Android M is released to the android open source project then They will also make a vanilla ROM running on this version.
Keep visiting this post for further Updates..
Source:Xda developers.