ArcFM Desktop 10.2.1a, and b, are only supported on ArcGIS Desktop 10.2.1. Furthermore, it is my current understanding that Esri does not support ArcGIS 10.2.1 on Windows 10. However, this might change in the future.
There is currently not an ArcFM 10.3 release, however the latest Object Reader and ArcFM Server releases (10.2.1b) will support ArcGIS Server 10.3, and 10.3.1.
I can basically echo what Juul said. At this time, Esri does not support Windows 10 on ArcGIS 10.2.1, and thus the ArcFM Solution line of 10.2.x releases can not be supported on Windows 10. If/when Esri announces they are going to support Windows 10, we have a plan in place to act, but we can't support Windows 10 until that time.
Also as Juul said, there is no ArcFM Desktop release above 10.2.1 (which is the Utility release, on which Esri is releasing UTUP's).
We have been testing Windows10
for the past few months. Everything is working as should even the custom ArcGIS and ArcFM tools we built. I suggest building a test station before rolling out.