CONTROVERSIAL OPINION TIME!
I'm probably going to get some hate for this but the truth is I actually love Twilicorn and think she's a good idea. In fact I prefer Alicorn Twilight far more than unicorn Twilight. Yeah I know it sounds controversial but let me explain why.
Now Twilight represents the element of magic and Celestia states she never saw a unicorn with such raw magic abilities so unicorn Twilight probably has more powerful magic than any other unicorn. She is knowledgeable with magic and she reads books on spells like all the time.
Also the Elements of Harmony which are probably the most powerful artifacts in Equestria, not the entire world just Equestria. Each element has a trait and quality which are essential to friendship. Twilight represents magic which might be the biggest one. Even before she was an alicorn at the beginning in the series her element was embedded into a crown while the others are in necklaces.
In Magical Mystery Cure, Celestia lists the qualities of each element,"Since you've come to Ponyville, you've displayed the charity, compassion, devotion, integrity, optimism, and of course, the leadership of a true princess."
So this was planned from the very beginning of the series, it was her destiny to become greater than she was and spread friendship around. I think it would be less appealing to think her destiny is just to send letters about friendship to Celestia.
Now I know Twilicorn is considered a Mary Sue or annoyingly perfect but I don't find her to be annoyingly perfect. I thought besides her princess status and wings I don't find her to be much different or more annoying. I don't know why but I think she is less annoying as an alicorn.
And also it may seem she's going to ditch her friends but I don't think so. To quote Celestia,"What would the princess of friendship be without her friends". I think that makes sense. And if she was sending most of the friendship letters and whe was instructed by Celestia it would make sense for her to be an alicorn rather than one of her friends.
And Twilicorn isn't really accepted because she's an alicorn and others prefer only two alicorns Celestia and Luna. Because they were born as alicorns with immortality and more powerful magic. But I feel there are two kinds of alicorns. Alicorns that were born that way and were descended by deities or something and ones who turned into alicorns because of their powerful abilities but born alicorn or not they are all very powerful like Cadance and of course Twilight. And I actually love Cadance and I actually thought she was a good addition and I felt this show got much more expansive after Season 2. But anyway Cadance and Twilight spread love and friendship, while Celestia and Luna raise and lower the sun and moon respectively. Believe it or not I actually think love and friendship are more powerful and important than raising and lowering the sun and moon even if that world's earth doesn't rotate. I mean raising and lowering the sun and moon respectively takes like only a second once every day that's unimpressive compared to spreading love and friendship. Okay maybe Luna can enter dreams too but that's about it.
Also if Twilight became an alicorn I feel the ending for this show is just going to be better than if she stayed an unicorn because it would be really nice to see Twilight fulfill a big destiny as the princess of friendship rather than the ending being about unicorn Twilight just sending friendship letters until she dies.
So that's why I actually think Twilicorn is a good idea and that I actually prefer alicorn over unicorn. After Castle Sweet Castle I actually think Twilicorn is getting better and I thought this show felt so much more high quality and more expansive after she became an alicorn. Now this is just what I think and feel like but I felt I had to explain.