You can effectively hide text by moving it to another document, then inserting a link in the original document.
For example, you want to hide the details of the deprecated version, but still make them available if desired.
Deprecated version of product:
text to be hidden
Current version of product:
ipso lorem ...
Move the "text to be hidden" to a new Google Doc. Back in the original file, highlight the "Deprecated..." line, from the menu choose Insert->Link and select the new Google Doc. You have now created a hyperlink to the "hidden" text. It's not ideal from a workflow point of view; but at least it works pretty well.
Ideally an add-on could be written that pops up the hyperlinked text when you hover over the link. A nice little project; maybe I'll do it when I find the time.