I mean it's not like it's impossible to get Conker in. We've seen with enough support, stagnant characters (
) can be brought to Smash, it's just a matter of presenting Nintendo with the demand. If people continue to not talk about Conker, he just probably won't get in.
Although Conker lives in Banjo's shadow, I'd argue that Conker is the next face of Rare after the bear given how much attention he receives from Microsoft. Plus, it's not like Banjo is the only one getting Totaku figures and stuff like that (gotta order my Conker one soon!). Whenever Rare/Microsoft promotes stuff, you can always bet Conker is gonna be right there alongside Banjo.
I'd say the only thing that really separates Banjo and Conker is popularity. Otherwise, they've both appeared in the same number of games, originating in Diddy Kong Racing.
This isn't me trying to advertise, but if you some of you are interested in Conker, don't forget the Conker thread exists and remains pretty active for a less popular character.