I think Scarlet & Violet work great as titles, even if they're not something super obvious. The words go well together, the colours are a nice throwback to the first gen, but them being "fancier" colours than red/blue/green etc makes them stand out.
In terms of future pairs, some ideas that could work:
Snow & Sand (would be great for a region with a big focus on exploration and a wide variety of environments, from beaches to snowy mountains)
Earth & Wind (based on the two of the four elements other than Fire and Water, which are already Pokémon types)
Metal & Wood (based on the Chinese elements, would be perfect for a region based on China)
0 & 1 (for a futuristic/sci-fi region)
Stuff like Dawn & Dusk or Sea & Sky could work too, but would be too reminiscent of other games.