I've recently purchased this router and like many others I've got dissapointed that the GPL code provided by TP-Link is pretty useless since it doesn't really build. There are too many patches that fail and packages seem outdated. I will try fixing the original GPL code, but now I came up with another idea: upgrade it to openwrt-18.06 with all the packages since it would build way easier. And it did. I've also moved lzma-loader and other image-compilation related stuff into it. So in the end I was able to produce an image with kernel 4.14 using the same mtk linux target. Unfortunetally I was not able to flash the router with it. It got rejected and I don't know why.

 So I would have multiple questions (just in case anyone can answer):

1. Into what kind of critereas should the image fit in to be accepted by the current firmware? Will it accept 4.14 linux kernel?
2. Can you actually flash the firmware instead of upgrading?
3. Can flashing/upgrading be done in any other way than in the web interface?
4. If the device gets soft-bricked is there a way to unbrick it?

I've created a git repository to store my efforts of creating a custom TL-R470T+ v6 openwrt image that would actually work. I'm not sure if I'll succeed, but maybe someone else could start of where I'll finish. 

Oh and yeah I know about the warranty and all that, so please..