The Switch reached everything possible in Japan and will end around 38- 40 million! It will do ~ 1,5- 2 million this year! What more could we want?

Well, assuming that the Switch 2 isn't agregiously expensive, and the backwards compatibility is decent, wouldn't you rather just get that over the original?  So I assume 'lights out' refers to a sudden decline in sales.

All Nintendo handhelds had a relativley good post sucessor afterlife. Why should it be different with the Switch? Switch 2 won't hit under 400$/€. You really think Nintendo would raise the entry level for their systems from 220$/€ (Switch Lite) to 400$/€+ all of a sudden? The Gamecube was not done until 2008 and that system was doing crazy bad in it's life!

Also, MH now has over 10% attach rate on PS5 even before we get to digital sales. Actually attach rate is probably somewhere near 20%.

The Switch should continue to sell and be shipped by Nintendo for quite some time.  But if we look at the top sellers for the Switch the OLED model is consistently the best seller, not the entry level console.    So if you are already spending that much on a Switch, it makes sense to just get the 2.  I expect to see Switch sales to decline sharply but not stop.  3DS sold for years! 

Fair enough. Expect for "sharply" i agree. The question is: Will the PS5 finally outsell the Switch in Japan for 2025?

Not likely, but possible.
Looking at the PS5 trend this year it's going to be in the neighborhood of 1-1.5 million while Switch is likely to be 1.5-2 million. If MH Wilds really raises the baseline for PS5 or Switch sales decline more sharply than I'm expecting, it could happen, but I don't think PS5 outsells Switch until next year.

Top 30 software now posted

Super Mario Bros. Wonder reaching 2 millions next week

The recent sales trend is a moderate YoY decline.  It's what the Switch has been doing for the past several years.  In fact it's % drop is even milder this year that it has been in previous years.  This idea that the Switch will hit a sales cliff this year doesn't come from the data at all.