Since i am working for meizu i cant share details.
Google hard you will get from some blogs.
Me and my friends  have ported some roms for xperia u.
based on stock firmware without unlocking bootloader using stock kernel itself. As we dont have money for support
Nor we were that famous in xda to get paypal donations. Any kid knows this do visit xperia phones threads in xda you can see hundreds of roms based on stock kernel and stock rom.
As for meizu phones i count 2-3 custom roms ported from stock which can be flashed via stock recovery update. Zip