Either as you are writing or after the fact you could move each sentence into the body of a note or as the actual note title.
Then, in a separate note you could just embed the sentences if you used the former method or simply add links if you used the latter. At this point you would be able just add the tags within the proper note.
In addition to this, if you wanted to tag an entire paragraph, you could embed each sentence note link or embed of a paragraph within a paragraph note and add the tag within that note and embed that within the composite note.
In case you were unaware, when working with embeds, it can be helpful to go split panes with the same note open in both. You can do your editing in one in edit mode while the other is in preview mode. This same method would be helpful if you went the paragraph note route except you would have the composite note in the adjacent pane in preview mode while you were editing sentence content in the sentence notes.
Hope this helps some. It sounds like a great idea. Thanks for the inspiration.