I love this game but one thing i dislike is that the only catch able legendary are mew, celeb and jirach. i feel legends would add more a challenge for players who have done everything you can. you should be able to catch every legendary by going through a group of trials. you should only be able to catch a legendary every month.
PROS: it'll add something new for experienced players to do.
CONS :it'll ruin the the pvp tournaments due to the fact that there wont be any good rewards to be sent out
PS: thank you for reading