Just to be clear, no one played "Halo DS" because it was a fanmade prototype that used a modded version of
GoldenEye: Rogue Agent [source - video evidence]. It was never released, and the only sign of its existence was an IGN staffer showing a video of him playing it - and never explaining his source for the demo.
Two Bungie devs came out and said that the Halo DS prototype was not made by Bungie, and someone may have made it for a pitch which happens a lot
[source].
Bungie has denied rumors of Halo coming to a Nintendo platform twice in the past
[source] [source].
I do think Halo on Switch was in discussion, but not because of the Halo DS rumor.