At this point in time during their respective years, the PS3, Xbox 360 and Nintendo DS sold through these percentages of their sales:
PlayStation 3 '15 - 44.9%
Xbox 360 '15 - 35.7%
Nintendo DS '07 - 24.7%
If each of these percentages were to hold for all 3 systems this year, these would be the estimated final yearly totals for all 3 in 2021.
PlayStation 4 '21 ~ 1,948,000 units
Xbox One '21 ~ 950,000 units
Nintendo Switch '21 ~ 31,713,000 units