I think the reason why Pichu wasn't wanted by the Pokemon Company to be in Melee was because it was a Baby Pokemon and didn't see it as a great choice, so Sakurai had to suggest it.
This could very well be true, but I don't think we were ever told how much of a push Pokemon Company made for specific characters pre-Brawl. It seems (as Pichu was primarily added to fill out the roster and not to promote the new gen) that the Pokemon Company didn't care as much which Pokemon were made playable. (Although who could argue with Pikachu, Mewtwo, and ... Jigglypuff).
Probably the reason why the Pokemon Company wanted Lucario in Brawl because it is one of the most popular non-1st gen Pokemons ever created and tons of people wanted to see him in Smash (not to mention heavy marketing that no 5th gen Pokemon can claim to have). Looking back on it, Lucario was a sure bet and he deserved to be in (I still find him deserving of a return).
I guess all we know for certain is that the Pokemon Company told Sakurai to put him in, although you are right in that we don't know if it was just due to marketing, due to positive reception and popularity, due to fitting well in Smash, or a mix of all (which is probably the most likely).
Had Mewtwo not been cut, I would say that Zoroark or a 6th gen Pokemon would be a shoo-in for a newcomer (much like how I would be shocked if King K. Rool did not get in this game). However, with Mewtwo still being promoted and possibly being the most wanted newcomer, I would still say very likely to happen, but a slight chance we may not get one. They could replace Lucario, but I like to think that Lucario is in a much different (and better) situation than Pichu and with Lucario still being used in promotion, I don't think the Pokemon Company wants him gone and I especially doubt Sakurai wants Lucario axed. Really, the only reason why I could see Lucario axed is due to time constraints.
It seems to boil down to if the Pokemon Company makes Sakurai include a rep of the newest gen first and foremost, before adding Mewtwo and/or Lucario. The preferable choice for us smashers would be for Mewtwo to get priority over a new character, however I still believe Pokemon Company will find adding a new character more important, and make Sakurai do that. That being said, I see the chance of getting both a new Pokemon and Mewtwo to be very high, as I think Mewtwo will be higher on Sakurai's list of characters to implement than he was in Brawl. I think Lucario would be relatively low on this list though, and might be in real danger of getting axed due to time restraints (which I agree would probably be the only reason he would be axed).
However if Lucario is axed, I do see him as one of the most likely DLC characters (if there are any).
That said, I don't believe promotion is necessarily a bad reason. It did, after all, give us Roy, even if it was for only one game (at least the possibility of returning exist) and it did help Fire Emblem 6's sales. It's also precisely why I feel a 6th gen would be a better choice than Zoroark or Victini; because the Pokemon Company has a perfect opportunity to help promote the upcoming gen. However, I don't believe newness, which is entirely different from promotion, is a good reason to include characters (nor relevancy).
I think promotion for promotion's sake is a bad reason for inclusion, although it does make sense market-wise, and I don't see it going away. However, Nintendo and Sakurai are usually smart with adding characters used for promotion, and characters chosen fit very well and are usually popular anyway (such as Roy, or Lucario -- if that's what he was added for). Promotion and popularity usually feed eachother and come hand in hand anyway (not always though). The thing is, if the "difficulty" with dealing with the Pokemon Company wasn't made as clear as it was, I bet alot of people wouldn't even think Lucario was added at the Pokemon Company's demand.
I also agree with you about the rep being from the most current gen, whether that is the 5th or 6th, I just had examples to work with from the 5th.
(odd how I both agree and disagree with your post)
That usually happens to me too when I'm debating with someone. Often makes it harder for me to disagree with them, lol.
Phew, that took me awhile.
![Embarrass :embarrass: :embarrass:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)