No matter what game it is, I've always kept my starter along my side as it always considered it that friend till the very end. Even before i got hooked with the anime, I always thought that the starter is something that I will never replace.
I do hope that in the future game, Riot Gamefreak will consider something extra for Starter pokemon such as always spawning with the best possible IVs to make them feel even more special since technically, a starter is something a player gets ONLY ONCE without considering breeding and trading. Then again, making starters always spawn with perfect IVs (or at the very least 3-4 perfect IVs on the right places) might cause some exploitable issues that I won't bother pointing out ;)
Regarding Yellow, dumping that Pikachu is an ethical issue. Even though that Pikachu is heavy yellow pixilated baggage at best (especially since you get Charmander, Squirtle, and Bulbasaur legitimately to carry your workload), i still can't help but keep it in the party, and at times even use it to clear certain fights and areas. Its even harder on a Nuzlocke run since that Pikachu, like every Pikachu there is, will always be too fragile to stand the heat of possible BS KOs from crithaxing rattatas.