One thing for sure, first Switch revision is already overdue.
DS/DS lite - 67 weeks
3DS/3DS XL - 74 weeks
GBA/GBA SP - 99 weeks
Average - 80 weeks
Switch/(today) - 98 weeks
It looks even better when you stack all Nintendo hardware by release dates, starting from GB pocket (1996). On average we've seen new system/revision every 62 weeks. Currently the last hardware released from Nintendo was New 2DS XL and it's been 79 weeks since the release.