I don't understood why people include Paper Mario in the Mario reps debate. If Paper Mario were to get in the game, he would represent his own Paper Maio series, not the Super Mario series. Paper Mario never had to worry about the other Mario reps.
Bowser Jr. is sadly a different case. If you couldn't tell by my avatar, I LOVE and support Junior. Ever since Brawl, I've badly wanted him in Smash. For the new Smash games, I felt like Bowser Jr. had a great chance of being playable: A villain character, unique moveset potential, important to Mario series. It seemed realistic..
Then came Rosalina. Don't get me wrong, Rosalina is an amazing character, and her moveset is very interesting. But when I saw "ROSALINA AND LUMA LAUNCH INTO BATTLE!", I became sad almost immediately. I knew Bowser Jr's chances had taken a big hit. I thought it was over for him, and I even stopped following Smash 4 for a minute.
But now, I'm feeling more hopeful, and I'm still supporting Jr, for reasons that have already been stated: Zelda and Pokemon had more reps than Mario in Brawl, so Smash 4 having six Mario reps is acceptable. Bowser Jr. could easily be revealed at E3, and he could come with Bowser's Castle, a stage that should've made an appearance in Smash a long time ago. He could utilize his paintbrush, gadgets and gizmos from the New Super Mario Bros. Series, various minions from his dad's army, and of course, his shell.
Here's one thing though that makes me think Sakurai has at least considered Junior before: the POTD where Waluigi was confirmed as an Assist Trophy. Sakurai stated, "Once again, Waluigi's Assist Trophy joins the collection!!... Which means he's not a playable character." I feel like this means Sakurai was aware of Waluigi's fanbase, since he made a point to say he was not playable. If Sakurai was aware of Waluigi, a character associated with the Mario Universe, he should definitely be aware of Bowser Jr. I would be surprised if Junior was only a trophy in this game, or non-existent entirely. I realize I'm grasping for straws, but I'm just trying to find some hope.
In conclusion, I love Bowser Jr, and I'm still going to support him until the very end. I know people find him annoying and unimportant to the Mario series, but the Koopa Prince will always have a place in my heart when it comes to Smash. I want to thank everyone else who supports Bowser Jr. I'm still gonna root for Junior, and I'll grasp for straws whenever necessary.
Long Live The Prince!