shop=office_equipment ? There is quite a lot of confusion with office/shop tagging so maybe more verbosity would be a good idea?

Or maybe https://wiki.openstreetmap.org/wiki/Tag:shop%3Doffice should be documented at wiki as perfectly fine value?

depending on what kind of office equipment - maybe shop=stationery or shop=furniture would be fine?

See https://wiki.openstreetmap.org/wiki/Tag:shop%3Dstationery and https://wiki.openstreetmap.org/wiki/Tag:shop%3Dfurniture