He has all the credentials to be an interesting character, though I have to ask: why is it only now that demand for him has become in any way vocal?
I think a large part of the reason is that a lot of people have finally come to accept that human Ganondorf in Smash will always remain a Captain Falcon (half-) clone, whether they like it or not.
In Melee, many were dumbfounded that Ganondorf was, of all things, a clone of Captain Falcon instead of being his own character. This especially stood out because he was (and remains) the ONLY clone of a character from a different series. When people heard that he was a last-minute inclusion, some people assumed that in the next Smash he'd become more unique to counteract his Melee incarnation.
Come Brawl and they were...kinda right, kinda not. He DID become more unique, but not to the extent that he was no longer related in any way to Captain Falcon in moveset terms. Plenty of people got frustrated, which I can understand, but this split Ganondorf's future in two--this was either a very, VERY slow decloning process to make players naturally adjust to a unique Ganondorf in the next game, or this was as far as Sakurai was taking it with differentiating him, since he might not have wanted to alienate any current fans of Ganondorf's current Captain Falcon-derived moveset that came about from his last-minute inplementation. Many of Ganondorf's fans were not fond of the latter option, so they held onto the very, VERY slim chance that the former would be what happened.
And now, with Smash 4 out, we can finally confirm the latter is what happened. While many Ganondorf fans were heartbroken, having had their favored character derive much of his abilities from Captain Falcon instead of mostly using his own abilities from Zelda games for 3 entries straight, it gave many of them a sense of closure on the whole ordeal. No need to hope for the possibility of a changed Ganondorf since it's been proven beyond a doubt that it will never happen no matter what, right?
This is where Ganon comes in. Pig Ganon I mean.
If Ganondorf fans won't see a version of his HUMAN form be unique, then they can hope that his more monstrous form can be a fresh, interesting character instead. This wouldn't affect Falcondorf's current fans, and it would finally service those who loved his incarnations from Zelda games proper. So his current (unfortunately tepid) demand, I think, correlates to many Smash fans getting over the grief of the confirmation of never having a unique human Ganondorf. Might as well look to new horizons and move on in new ways, right?
Personally if he were in Smash I'd like Ganon to mostly take inspiration from his A Link to the Past and Four Swords Adventures incarnations, with a bit of Yuga Ganon from A Link Between Worlds sprinkled in. A spear, fire bats, and eerie teleportation sounds really cool to me.