I recently came across a situation where I needed to talk to a user about further clarification about what his topic was about, to ensure that they didn’t disobey the rules. I initially started the conversation on the original topic, I then realised I needed to get into more detail and information and I didn’t want to derail the topic any further. My intention was to split the topic into a new message, I realised that this wasn’t available would it be possible for this to be implemented? As the aforementioned situation, I just had to split it into a new topic then make the topic a private message which wasn’t really ideal.
The difficulty is that you wouldn’t have access, as moderators don’t have access to PMs unless they are a part of the PM or the PM is currently flagged.