Thanks for your suggestions, ET. I agree it would be useful to have those features, but they aren’t available in the standard edition of the bbForum software we use.
As it happens there is a Preview button on the admin pages for moderators but it doesn’t work properly: it simply links to the current version of the page without showing any unpublished edits, so it gives no idea of what the changes would look like, and previewing an unpublished comment shows nothing.
I suspect if we wanted to implement new features we’d have to switch to a different WordPress plugin or use a separate CMS engine. That would be an enormous undertaking for the site admin, so I don’t think it’s likely to happen.
Correcting text isn’t a huge burden for the mods, because we try to read everything anyway and if we spot a typo it’s a simple task to press the edit button and fix it – in most cases, spelling errors are underlined automatically and can be fixed by selecting from a right-click menu.