During the most recent Nintendo Direct, it was announced that the Switch Online subscription service would be expanding in late October. The new tier, currently referred to as Nintendo Switch Online + Expansion Pack, adds a couple of extra classic console libraries. Specifically, the Expansion Pack will add an assortment of Nintendo 64 and Sega Genesis games.
Both of the new game libraries look to be starting off fairly strong with a solid assortment of beloved favorites. There are some notable omissions, but given how packed the N64 and Genesis libraries were, it's understandable that Nintendo wouldn't be able to include absolutely everything. Still, Nintendo did say that it's planning to add even more N64 games like Paper Mario and Pokemon Snap in the future. It also mentioned adding more Genesis games, but did not provide examples.