Yes, but couldn't it be, because the 85is and 90is are 100% identical (except the screen size) they have the same firmware.
I don't think the firmware is different. What should be the difference if only the screen size of the cameras differs. Also the resolution of the screens is the same.
Anyway. As soon as something is out for the 90is - I will check it with my 85is and report.
I'm positively looking forward that it will work.
... otherwise I would have to sell my 85is and get a 90is :-)
It would be worth just for the RAW feature. Because also in highest quality mode, there is a JPEG compression highly noticeable if you zoom in (on the PC)