Would it make sense to implement a plugin interface that is compatible with Xrm Toolbox plugins? Instead of re implementing all of the functions already available we could use them from within visual studio. As long as you don't actually copy their code I wouldn't think that licensing would be an issue.
With that said, the ability to modify OptionSets, Convert one type to another, convert local to global or rename an attribute all sound like useful features. I'm not too worried about bulk updates as there are already tools to do that and it doesn't seem to fit as much into a developer tool set to me.

As this suggestion is still in the design phase I would like to solicit feedback regarding this suggestion, along with anything related to the editing of attributes and entity metadata. Planned for v5 is the ability to download and save an entire entity along with its metadata to a file. All changes will be made offline to the file and the publishing of any changes will occur all at once. Some ideas being considered are:

Ability to quickly create/modify optionsets.
Ability to update attribute properties in bulk
Ability to convert an attribute to another type
Ability to convert a local optionset to a global optionset
Ability to create a cloned attribute and copy the data over to the new attribute

Your thoughts on these ideas as well as any other that fit into this area would be greatly appreciated.