Panasonic DVD-RAM drive LF-M821JD (SW9574C) is now sold in Japan.
16x DVD+/-R, 8x DVD+RW, 6x DVD-RW, 4x DVD+/-R/DL, 5x DVD-RAM with cartridge. Book type of +R and +R/DL is automatically changed to DVD-ROM. 16x/8x writing is Z-CLV.
Here is scan results page of LF-M821JD.
16x writing speed is: