I think surely all special techs and hero techs will be unique, while standard technologies will stay common.
For instance, I just committed a big change to the Ministry with an all-new tech tree and all-new tech icons, while the common Forge tech icons remain the same as other civs.
A nice improvement for techs and their icons would be to allow a _civ or {civ} element in the icon line of tech files: https://gitea.wildfiregames.com/0ad/0ad/issues/8734
This would allow for techs to look unique in the UI, but underneath still be common among civs.