can I ask if any evidence has ever emerged to indicate MH 370's final 08:11hrs ping was emitted from a point on the southern arc rather than the northern arc?
No.
The problem is, no one starts a thread like this and expects it to go this long. I've seen this on every site I've been on.
If people really want to keep discussing certain aspects, such as the Inmarsat pings, I would suggest you break up the topic in different threads. It's been working on other sites, and it tends to break up the clutter of regurgitated theories and questions.