Looking forward to the comparisons.
The DS did 20.55m in 2010 according to VGC estimates. That's a weekly baseline of ~300k followed by a mitigated holiday boost because the original plan was to have the 3DS launch during the holidays of 2010, resulting in a weak holiday lineup for the DS. Basically, even if Switch should fall behind the DS sometime during the year, it can easily make that back late in the year because the circumstances for a successor differ significantly and as such the planned software release schedule does too.
When I say baseline of ~300k for the DS, this includes stronger weeks early in the year (~350k) and weaker weaks during the summer (~250k).