As it turns out, you can already select the factories of a selection group:
(1) CTRL + number to create selection group (of factories) (2) number to select produced units (3) CTRL + SHIFT + number to select producing units (factories)For (2) and (3), if you press the number twice then you go to the selected group in question with your camera. This is fully functional in the base game, with no UI mods enabled. As @Meltdown mentions:
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edit: a moderator can close this topic now.