HTTP and HTTPS in one VS

Technically yes, but it would be very difficult and I don't really think that's the point. A forward proxy will attempt to first resolve and then directly connect to the remote Internet host, and on the origin port. Unless I'm still missing something, you'd either have to 1) modify the proxy to resolve all remote hosts to the LTM VIP, and then have the LTM perform the real DNS lookup and forward the request, or 2) put the LTM in forwarding mode, in which case it wouldn't matter what port or protocol was going through it. In no case can I imagine that the forward proxy would forward traffic to another device on the same proxy port (8080).