I prefer catching them all over seeing them all for the challenge, but for the remake I'm hoping it will convert to the way we had it in Diamond/Pearl/Platinum to rather see them all. It'll give the game more of a benefit, as you know they'll need to put in extra trainers to the game, they'll need to change the variety of the Pokémon people had from before in order for us to see them, and it means a better chance at training as you won't always be battling the same common types of Pokémon over and over again.
In addition, having to see them all will give us gamers an easier chance for getting the National Dex as well. As long as they don't make it like FRLG where you had to have a certain amount of Pokémon to get specific items, I'll be fine because that was just too hectic, especially if you wanted the EXP. Share in the game to make training a little bit lighter on us.