I think there are many possible things you could add as a new starter. First of all, pikachu needs to be added, because it was the starter for 1st gen games. Another thing could be a special bonus starter for joining on a special occasion, such as Christmas, or Halloween or something. The color of the pokemon could be relavent to it, too. For example, you join on halloween, you get a shadow Lampent.

You can obtain pikachu on maps so that is not needed. And special starters would lead to mass account creations w/ proxy's trying to obtain one.

Very good point cause many people will want to creat as many account as they can and give the starter Pokemon and the other Pokemon for this case let's say shadow lampet to there original account and who would want that if that happens all types of colored Pokemon would not be rare and maybe one dude will have over 1000 shadow Pokemon of the same species

There are special events for those holidays, you have to play the events in order to get the prizes.