Totally agree on the Phone and the Radio. They were two of my favourite features of GSC and I was so disappointed when they were dumped in RSE (along with night and day, although DP brought those back).
One thing I'd like... it's a little odd, but I'd like the "New Pokédex" back. In GSC they didn't talk about regional pokédexes, just the "old" and the "new", the new having all 252 in a more sensible order that put like with like. Then obviously in the Advanced Generation they decided to dump this model because it'd need constant updating, and went with the National Dex (which then gets especially confusing when IVth gen dumps a boatload of extra prevos and evos on old pokémon).
But I liked the idea if the New Pokédex. I liked Pichu being next to Pikachu and Raichu. I'd like to see them put together a revamped IVth generation "New Pokédex" with Gallade next to Gardevoir. Just my little dream...