You can xflash Q120A to Liteon 160P6S
You can xflash G120A to Liteon 165P6S
Xflashing 160P6S to 165P6S apparently does not work. So, why should Xflashing Q120A to G120A work?
2) will DVDRAM suuport appear?
Not necessarily. But as xflashing is not always successful, this question is academic. Some people say, that early 160P6S were DVDRAM capable drives, that didn't pass quality control.
3) which one is better for reading/writing or have they the same quality?
They are basically the same.
4) have they riplock for dvd-video?
Just have a look into the reviews. Except of some features 6S series should behave the same way regarding reading capabilities.