Characters should have adjusted heights [Pikachu should not be as tall as Ichigo and Link] Agreed

A character talking about other SSF2 fighters like Snake in Brawl or Pit in the new games. It's called Smaash Taunt, it's not always used to analyze opponents.
A couple of ideas could be:
Pikachu: Taunting would open up Dexter the pokedex giving entries on them I don't really see this coming, to be honest. Altough I think it should activate Pokémon Stadium's Narrator to comment on the Pokémon Colloseum stage.
Fox: could have Slippy, Rob, or Peppy analyze the opponent None of Star Fox's Smash Taunts in official Smash games analze opponents. They just talk about the state of the fight.
Link: could have Navi Considering that a lot of Zelda fans hate Navi, I don't reallly see this coming.
Sonic: could have his friends talk to him through that pad thing like in lost worlds No, just no.

Easter Eggs would be a very nice
Like everyday that a demo was released when you go to the animal crossing stage you see the devs in the background in an animal crossing style instead of the animal crossing characters. What I mean by everyday demo release is that every day that one of the demo in past was released it causes this Easter egg. If the demo v0.1 was released August 1 and v0.2 was released on September 2 then both of these days would occur this Easter egg. At night you see someone from the SSF2 music department play the SSF2 theme instead of K.K. Slider. Nope. I'm pretty sure Devs said that all Past Stages would behave exactly like their Smash counterparts. And Animal Crossing characters would fit a lot better in that stage.

If Sonic enemies are added in then Sonic and Tails [Knuckes and Shadow to if they do get into the game] can defeat them just by jumping into them No. This would make them have an unfair advantage over other characters. Completely breaking the game's balance.
And etc. of the rest of the eggs.. But I would like see some eggs put into the game

Comments in bold.
I will admit, I also want to see Easter Eggs in the game, mostly because they just show how dedicated the Devs are.

The Pokémon Stadium Narrator inPokémon Stadium was basically the commentarist of the game that spoke trough the battles like (Pikachu used Thunder!) Or something like that.

Color Palette Program: Where you can change the color appearance of a character to make it a custom sprite.

Competitive CPUs: In Smash 4, we've seen how the Amiibos work and the way they level up. What if we tried to level up stats for that CPU so they can have a difficultly as a Highly Competitive Smash Player can.

What do you think?

A character talking about other SSF2 fighters like Snake in Brawl or Pit in the new games.
A couple of ideas could be:
Pikachu: Taunting would open up Dexter the pokedex giving entries on them
Fox: could have Slippy, Rob, or Peppy analyze the opponent
Link: could have Navi
Sonic: could have his friends talk to him through that pad thing like in lost worlds

I think that the infinite jabs that Kirby, Fox and the other characters that have it should have the Super Smash Bros Wii U jab end. Where Fox does his flurry of kicks but ends it off with one hard kick.

Another thing I could like to see put in is character exclusive wins in certain match-ups. Putting in animations or voices that can only be heard if you defeat a character with a certain character. An example of the matchups could be Mario and Bowser or Sonic and Tails.

I agree with both. Except for the examples you made in the second suggestion.

Well they are the easiest examples that I could give so that's why I said them. What character matchups would like to see with a unique animation during the end of the match menu?

Fox and Falco (If he gets in) and... that's all I can think of (tough, I'd like to see some Fire Emblem ones, just like Smash 4)