I personally think that Ho-oh and Mew haven't been giving opportunities to show there posessive abilities.It would be a great idea, if Nintendo intended for Mew to be the most powerful Pokemon of all, but mistakenly created Arceus that overshadowed Mew story-wise and stat-wise. I was thinking maybe turn mew +20 spatk +20 speed +20 hp also featuring new ability "Descend" were in game its type change every turn during battle making opponent diffricult to use supereffective moves, (this ability will only exist for Mew "note*" if Gamefreaks or Nintendo wants to confirm Mew is the ancestral Pokemon), and making it red seperating if from its shiny blue color, if you want to keep the small cute image everyone loves.
Ho-oh wings can turn into fire to larger wings bigger beak with a serpent appeal to its head area and a much wider movepool, also possibly give it another dual type like: fire/rock of flying/fighting.
Game-wise, Mew will turn alternate when you obtain one take it to the tree of beginning with Ho-oh in your party behind Mew, and Ho-oh will turn to alternate forme when near the tree of beginning with Mew behind it. but anime-wise Mew and Ho-oh will have a good opportunity to finally show there true nature or power to be exact inh a new movie that will show us more evidence of Mew and Ho-oh's true existence.
Please comment on what you think about my ideas, and if you disagree, dont hesitate to share your ideas. *.*