> What about middleboxes I want to employ myself, e.g. to watch my own traffic?

> Except I don't have control about the edge nodes either, because the one edge is a remote server while the other edge is a locked-down smartphone or IoT device.

If you don't have control over either of the endpoints, is it really your own traffic? Going a bit deeper: if you don't have control over your smartphone or IoT device, is it really your smartphone or IoT device?