About terminology: we need to differentiate capturing (buildings), conversion (age of empires priest) and capturing sheeps. For scenario making, it would be also useful gaia conversion units like aoe2 (when a human units reach gaia units, they are given to that player)
Capturing it's working. IRC initals plans were against conversion (with one roman hero ability exception), but there was in mind sheep and female capturing (the later as wow said, seems to have been discarded).
Wololoing would be useful for modders: @Lion.Kanzen, wasn't a working version in Aristeia? It could be added to the engine without using it in the 0 ad main game. (Or just a scenario only priest for showing)