Dropbear is installed in the main image.
Default iptables does not allow port 22 inbound from wifi but makes no restrictions on traffic over usb0 (usbnet).
@GM: You might check if a "stock" Kpw will let you get usbnet running in 'main' - then ssh access should "just work". No JB required (unless required to get usbnet started).
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Consider this post "excessive whitespace" - I should know you already have a six month or more backlog of things you want to try out already (and this is probably one of them).