---Gen 3---
1983 - Famicom
1985 - Sega Master System
~3 Year Gap~
---Gen 4---
1988 - Sega Mega Drive
1989 - Game Boy
1990 - Super Famicom
~4 Year Gap~
---Gen 5---
1994 - Sega Saturn, Playstation 1
1996 - Nintendo 64
~2 Year Gap~
---Gen 6---
1998 - Dreamcast
2000 - Playstation 2
2001 - GameCube, Xbox, GBA
~3 Year Gap~
---Gen 7---
2004 - DS, PSP
2005 - Xbox 360
2006 - Wii, Playstation 3
~5 Year Gap~
---Gen 8---
2011 - 3DS, PS Vita
2012 - Wii U
2013 - Playstation 4, Xbox One
~4 Year Gap~
---Gen 9---
2017 - Nintendo Switch
Makes the most sense thus far.
Now, (pertaing to the OP) once PS5 and XB4 launch, vgchartz might only have Nintendo Switch, PS5, and XB4 as the currently selling consoles to track sales for on the front page for some years on end.
Going from tracking 5 systems, to only tracking PS5 and XB4 would not make any sense.
As far as aligned analysis on vgchartz, Gapchartz has already taken a generational agnostic approach and is comparing the Nintendo Switch to Wii, DS, 3DS, and PS4, and will probably add PS5 and XB4 to that list of comparisons when that time comes.
