I found this while pondering an easier way to create a sprite for an interceptor for the battlescape (see
https://openxcom.org/forum/index.php/topic,929.msg9043.html#msg9043 )
you need blender
https://www.blender.org/and I would suggest using irfanview
https://www.irfanview.de/both are also available as portable apps
https://portableapps.com/here in the independent gaming forum, user "Rock D" posted something very helpful: a blender file that allows you to create isometric views for a given 3d model. what it does is it rotates a camera around the object in the correct angle and distance and stuff, and takes snapshots. for our purposes, the snapshots are too large and too many, but you can easily choose the right ones out of there and batch-convert them using irfanview.
so once you have a 3d model, you can turn it into sprites easily. and if we ever go high-res, the 3d models can be used again to create high-res sprites