Well it does turn out that if a group checks TextOnly in MessagePolicies, there is no ReplyToSender footer link included now, so in essence, a text-based email group is missing out on some functionality not really directly-related to HTML or plain text content.
The other weird thing that I discovered while testing this and possible combos, using info provided in the manual, you are allowed setting this particular combo which seems conflicting at the very least:
Maybe it's wording but only one of those should be allowed to be selected at a time, clicking the unchecked one should check that and clear the other.
Turns out when both are selected the plain text wins. I'll post it on beta.