From xiaomi and 4pda.ru: ssh need developer firmware, or some 2014-15 old stable rom.
p.s.: Successfully installed ssh with developer rom from xiaomi official page!
0. You need download developer rom from Xiaomi page:
http://www1.miwifi.com/miwifi_download.html Rom section Update your router manually from routers local web page.
1. You need
download official miwifi_ssh.bin file from https://d.miwifi.com/rom/ssh
It is important to login with your Xiaomi account and having the router registered under it (best way is with the android app, google it, I'm not going to spend time on this here) as the file is personalized for your router and the page will also tell you your root password.
Procedure to flash miwifi_ssh.bin:
1. copy miwifi_ssh.bin on the root folder of a FAT32 formatted USB key.
2. disconnect the power from the router and connect the USB key to it. Do not connect before power off, or it will recover the original firmware! (for me recovered 2.6.103 int)
3. keep the reset button pressed while you connect the power, release the reset button when the router orange led starts flashing.
4. wait 3-5 seconds, router will restart and SSH will be available on port 22. WinScp works too! Username and pass same as your on
https://d.miwifi.com/rom/ssh was!