Well I guess I'll be the first to suggest it, but
Seeing as how Nintendo Packaged the Animal Crossing DLC within the NSO Expansion, (even if you can get it separately), we could start seeing this for other games. Could the Next Smash Bros. be one of those games?
Assuming the Next Smash is in Planning (which it likely is), and NSO continues on to the next console, I could see Smash DLC being offered at no additional cost (as long as you're subscribed) being a Big Selling point
Like imagine the Next Smash is coming out, and they have it to where Master Chief is DLC for that game, but if you get the $50-60 Premium NSO service, you can download him at no Additional cost, along with the other perks like Online, the Old consoles games, etc
I guess the main hiccup is that Since I Imagine alot of the DLC for the Next Smash game to be 3rd parties, I wonder how the 3rd Party companies would feel, or want to be compensated for their characters potentially being potentially obtained through this method. If Gamepass is any indication (as well as NSO Expansion itself), Nintendo would have to pay either a fee or royalties to any Companies involved, in addition to the Agreements made with selling 3rd Party DLC Characters normally as well. I could see Nintendo seeing worth in it considering how Popular Smash DLC is