Amiibo researchers are almost certain that the next DLC update will come before the Dark Samus and Richter amiibo release on January 17th. Why? Because they require a patch to function. Let's shed some light on the subject!
At Super Smash Bros. Ultimate's launch, all existing Smash amiibo figures were compatible with the game through their respective series' amiibo. Newcomers to Ultimate sometimes did not have existing amiibo compatibility, such as Dark Samus. To remedy this, Nintendo patches the compatibility into the game alongside content updates prior to that amiibo’s release. Update 2.0 added Piranha Plant, King K. Rool and Ice Climbers amiibo compatibility into the game, and update 6.0 made Simon Belmont and Incineroar compatible. Nearly every update has occurred less than two weeks before the amiibo’s release, with the only exception being the 3.0 update.
Nintendo does this to ensure that by the time the amiibo hit shelves, they'll be functioning properly in Ultimate. This also means something else: an update must precede every amiibo release. Every single time a new amiibo comes out, a patch always drops at some point beforehand that includes DLC. Knowing that Dark Samus and Richter have no amiibo functionality in the game (An explanation of how we learned that can be found here), then we should expect a patch of some kind (not necessarily DLC) by January 17th.
January 7th edit: This prediction was indeed correct! Update 6.1.1 patched in Dark Samus and Richter, but nothing else. This is the only time that an amiibo's compatibility has been added to the game without other content being included as well.