SK53
Given that OSM allows free-form tagging and that the wiki is not a specification allowing yourselves to restricted by current values is probably counter productive. The building tag is building:type, the use of ":type" long post-dates the other usage for most tags. If your interest is current building use then fine, but mine is architectural, so I'm interested in churches whether they are still in use as churches, as gurdwaras, pubs or housing. More importantly the architecural form of the building is the property which is most easily recognised in the field. The buildings in Chester Street look like houses not the offices which they have long been. The Piano & Pitcher in Nottingham looks like a church from half-a-male away etc.