Adapting the scale, direction, offset etc. while uploading is a great idea. I just learned, some checking is done client-side. Some settings are difficult to find. So we should have a way to change them afterwards. It may be good, to keep the original model file to apply corrected settings. - A good way to check them would be a WYSIWYG 3D viewer, like OSM2World, just the new model and some more around.
Agreed, the single 3dmr tag with all settings is not handsome. For a way side cross or a bench, a direction value is quite good. A scale or height if the model is something like a three or a lantern. We must consider not to mix up with the existing tagging. The Eiffel Tower will not have a direction now. We could use 3dmr:direction too or set an extra node at the same place. But using the original node or relation will help, to “hide” the OSM parts, replaced by the model.
The tagging is not really a part of the Model Repository, the tagging will be recommend only in the description.
The Repository already has geographic positions for each model now. For the TARDIS this may just a famous example, there will be more in OSM.
Yes! And if there are more but one, a relation has to be added! The 3dmr tag(s) go to the relation (only) “keep it simple”