How would it not be a challenge mega evolution is part of the pokemon world and its not like level 1 guys should get mega stone it would be rare and when you acquire it you would probably use it on e4 or pvp. and this would change the whole structure of pvp and make it more interesting and fun

I couldn't say, I stoped playing pokemon games before mega evos. Some pokes are already unkillable like regenerator slowbro I can't imagine it with mega, but yeah could still be interesting if the mechanich is balanced

Thanks guys for all your positive answers and thank you for informing us that mega evolution will be implemented