I'm wondering if scripting could get around the problems and generate unrest for us. Then we could replace all religion_unrest symbols with the normal unrest symbol, and make it transparent what is religious and normal unrest. Then we could use all 7 religion slots available, and automatically generate our unrest, but it would have some negative interface consequences.

Alternatively, we could put 3 dummy religions first, which would have no usage in-game, then 4 unrest-free religions afterwards, for which we use scripting to generate unrest. The latter would look better in-game than the 7 religions system would, for a number of reasons, so we have the choice of either 3 religions which would be easy to implement, or 4 religions that would be difficult (hopefully not impossible) to implement. If we choose 4 religions Christianity-Islam-Paganism-Judaism would probably be the best choice IMO (if we can't have both sunni-shia and catholic-orthodox using only one of them seems strange). If we can have all 7 we could again use Catholic-Orthodox-Judaism-Shia-Sunni-Asatru-Shamanism.