I think that would be a bit of a stretch. Currently, there are only 4 alicorns.
If the rest of the Mane 6 became alicorns, there would be 5 more alicorns, more than doubling the amount of them! Can you imagine NINE alicorns? That would be complete mayhem!
Plus, what would they be the princesses of? The princesses have very important things to take care of, like the Sun, the Moon, love, and friendship. Sure, you could go with their Elements of Harmony, but those relics are long gone now. They probably wouldn't be very important things to take care of, anyway. They already do their elements in their everyday lives. After all, Pinkie Pie always makes everypony smile!
Now, I will say more things in response to these posts!
Oh no, making lots of fans very unhappy just for the sake of selling some toys. I don't think it would be a very good trade-off at all, in my opinion. I can imagine all the outcries of the fans for doing that. I would be pretty unhappy too.
Basically, from a practical standpoint, it'll never happen.
Exactly.
Yeah, I don't think the toys will make much more sales from the new change. It fells kind of anticlimactic and would probably backfire on them. It could even net them less sales.
And making them all have horns and wings doesn't really promote the "friendship" part of it, as it doesn't bring out the weaknesses of the characters as much. (Take a look at Dragonshy.)
It might not be completely out of the question, but, like I said, I think it would be a little bit of a stretch. However, your reasoning makes me see that it's definitely possible though.
But with less contact with Princess Celestia in the newer episodes (no letters, friendship journal abandoned), and less dialogue shots per season (10 in S1, now just 4 in S7), it doesn't seem likely. Plus, I think 9 alicorns would be way too much, and lower the value of being an alicorn by a little, but enough to make it feel kinda cheap.
However, I like the idea of the second idea! But you're right, it's a completely different topic.
The thing is, I think that if one of the Mane 6 happened to die, Princess Twiilght could probably revive them with her magic and make them functionally younger again. It wouldn't be necessary. (Yes, I think magic can be used for healing/reviving.)
I want to say something here, but I'm afraid I'll spoil the Season 6 finale...
Ok, that's all for this post. Goodbye!