The idea of having all the Pokémon being able to follow you over a certain selected few I think is a better suited idea for the game. Yes, it'll seem a little strange having some following us [like mentioned Magikarp, Wailord, the legenderies, etc], but at least it'll add in some humor to the game. Not to mention, it'll lessen the amount of complaints people may have about how they cannot have their favorite Pokémon able to follow them, but only a selected few or simply just the starters.
I like this feature nonetheless and it not only brings in great remanents of the original GSC, but also Pokémon Yellow too. Being able to talk to our Pokémon and see how they are feeling is another beneficial factor and it'll be amusing to see what a "God" Pokémon like Arceus will be feeling while following us. Though, for me, I'll more than likely have my favorite Pokémon following me around such as Pichu, Houndoom, and a few others. Then, of course I'll have the odd ones following me as well for the laughs and fun of the game.
Overall, a plus for the remakes and something I'll enjoy knowing we;ve finalyl got full confirmation about this factor seeing as how it was so highly speculated beforehand.