Regarding point 5, the front-end doesn't need to support pipelining at all, and the back-end doesn't require it either in most cases. Regarding chunk support, yeah you could patch this by disabling chunked requests on both systems, but if only one system disables it that pretty much just makes the situation worse.
I think your first point could be misread. If you have a front-end and a back-end, and they talk to eachother using HTTPS, that's exploitable. What's not exploitable is when you don't have a frontend at all, or your frontend isn't doing any kind of request parsing (ie it's a network load balancer).