After some discussion in Freilichtmuseen - wie taggen? - #17 by Rogehm i changed the museum tag because there was confusion on how to tag a open air museum and so on. So i clarified and changed the english and german version accordingly.
Now the user User:Rtfm - OpenStreetMap Wiki changed it to something i think is wrong and more importantly seems to be nowhere been discussed before. The site they changed it to was created yesterday - by that same user. Key:museum:type - OpenStreetMap Wiki
he also added a deprecation template to museum_type (overall I think it is ok, although there are some values which aren’t in use for the suggested replacement operator:type)