*I DID NOT LOOK AT THE REPLIES TO THIS POST, I AM FAR TOO TIRED TO DO SO*
I enjoyed your post, as it was well thought-out, very interesting. You really made your points.
However, I think it's entirely possible to improve the next installment, if it ever takes place. I never thought of an adventure mode for Smash, I never thought of a stage builder.
Still, though, the only other developer who could possibly rival Sakurai, in my opinion at least, is Shigeru Miyamoto. But even then, he just doesn't... ugh, I just can't put my finger on it, but he just doesn't... have that TOUCH that Sakurai has... I dunno.
There is one thing we should remember though-- Nintendo is a company. So far, a leading company in the gaming industry. How? Money. How do you get money? The best way would be to make a really awesome (or at least popular and appealing) game that everyone buys. Smash Bros. is undoubtedly one of Nintendo's most popular franchises, and they know it. So, even if they are lazy when it came to ideas and development, I'd expect them to make a new installment, or maybe even an update, like you said.
If I missed one of your points, I apologize, I am very tired and haven't been able to think very thoroughly today.