When will Apple add support for Nintendo Switch 2 controllers?

they are not really a company know to share their long term plans really

if it was me then I would try to suggest it to them

Product Feedback - Apple

or reach out to their official support channels

Get Support (apple.com)

And or

Contact - Official Apple Support

And or

Contact - How to Contact Us - Apple

Or

Genius Bar Reservation and Apple Support Options - Apple

On this user-to-user site, we are all users......just like you. No one here would have any information about what Apple might be planning or when they might do something......unless Apple has published the information.

Apple does not tip their hand, so the best that anyone could do in the way of "information" would be rumor or speculation.

Another way to say the same thing:

Those who really know, cannot say. Those that say cannot know.

Apple invites submission of comments and feature requests via its Product Feedback portal. If you would like to see support for additional controllers in a future release of iOS/iPadOS, this would be the most appropriate channel to make a request.

Feedback - Apple