[JKT]

Fwiw, there are ways to achieve this with keyboard shortcuts (that isn't to say that having a way to do this in the context menu wouldn't be nice, but in the meantime...):

If you highlight a word and press command-shift-F it populates the search field in the toolbar with that word or words (the limitation here is that you will need to first select the search engine you want to use prior to populating the field).

Highlighting an URL and pressing command-shift-U will open the URL in a new tab.