I’m really…disappointed…irritated…not surprised. Nintendo has an amazing back catalog and this is what they give their fans…
The days of the Wii Virtual Console are long gone. The landscape has changed too much; some companies (notably Capcom and Konami, both of which have a huge presence in the NES and SNES catalogs) are releasing their own retro collections, which likely takes Castlevania, Gradius, Street Fighter, Mega Man, and other game series out of the running for NSO inclusion. And that's not even before we get to the licensed games both of those companies did (the Disney stuff from Capcom, Ninja Turtles from Konami, etc).
SEGA has released the Genesis mini and will likely release at least 3 more Genesis collections on a variety of consoles before the generation is over

. So that likely takes out the Genesis entirely (the Genesis was a prominent console with lots of games back on the Wii Virtual Console).
Neo Geo games are being released individually, so they're not candidates for NSO.
So I think all of that means that the main guarantee from NSO are Nintendo first-party games for whatever consoles they have available, and other "bread crumbs."