Early 2015 MacBook and late 2015 iMac 27'' 5K, target display mode alternative solution

Late 2015 iMac 27 5K doesn't support target display mode anymore, so early 2015 Macbook could not use it as display with target display mode.Plus This model MacBook doesn't come with thunderbolt port, one USB-c type only.

Obvious workaround will be old fashion remote desktop then. Apple's remote screen works, but it could not scale and the screen response depends network condition if it is via WiFi.

Then I got a Apple Thunderbolt 3 to Thunderbolt 2 adapter from BestBuy, however MacBook won't recognize it at all. Called Apple support couple times, and eventually they told me the usb type C port on this early 2015 MacBook is not really Thunderbolt 3, it is just USB 3.1 Gen one,  and 5Gbps is its maximum bandwidth, so the adapter won't work for it, and I could not use it for thunderbolt 2.0 conversion at all. (This is from Ajay Divakaran post on http://www.ajaydivakaran.com/imac-retina-and-target-display-mode/)

This leaves me to another try with USB 3.0 IP networking. after a good amount of google searching, I found one USB 3.0 cable with build-in switch: JUC500 from J5 Create. It is used for file transfer between two computer with USB 3.0 via smart Data Link protocol. (I did think about USB 3.0 cross over, but none of them available could be used for data transfer) I found the driver for IP over USB on OSX via HoRNDIS, which was build to share internet connection via USB cable for OS X, since Apple never provides its own driver for it. This driver was written some years ago, so it is for USB 2.0, and it is halfplex for some reason, so iPerf shows around 240Mbps throughput. I could not blame them at any rate. They was build to do they was meant to do, but not my case here. :-(

Eventually I went for ancient old cross over Ethernet cable with 1Gbps bandwidth, and of course I need a USB C to ethernet adapter for MacBook as well from eBay. This good old fashion connection was recognized by iMac ethernet port and Macbook USB type c port right away. With their own private subnet, 1Gbps connection via VNC connection (scaleable) could be an acceptable alternative for the missing target display mode finally.