This would likely be a site admin task to add the site specific styles.

It would be good if the addition of the new text styles was as simple as eg. adding of new gadget definitions (instead of having to code long javascript code to add new items in the list)

example:

• usage example | <span class="usageexample">{{{1|usage example}}}</span>
• definition | <dfn class="definition">{{{1|definition}}}</dfn>

etc.

To confirm, is this is asking for a tool to wrap selections in templates?

formatting bar

I'd say that this may be wiki-specific, but it should also be possible to make it global.

For now, we don't have global tools, but we should have them (T121470). For tools that are global, this definition should be as global and unified as possible.