As Dimitri said, getting the base game ready and the first bit of story mode up and running is more important than adding another character. Some animation work and balancing still needs to be done in the main cast as well, for the eventual 1.0 release. Most recently, the biggest necessity was getting Tutorial Mode put into the game, and it's now there, and ready to be updated for future balance changes and roster additions. And it also goes without saying that the personal lives of key dev members has been putting a hamper on things, which they've been very transparent about.
What it comes down to, though, is to try not to look at the game, or any fighting game really, based only on amount of characters that are in it. It's a fool's bet. Keep in mind they'll also need to get the Mac and Linux versions going as well, which will take priority over Goat. You will get Goat eventually, but the game itself getting into its best state is more important, otherwise future characters aren't going to matter one bit. This goes for basically any fighting game out there. They can't just be a mad rush to add more and more and more characters. Making a great game takes priority, at least with Mane 6. This should be seen as a good thing.
And one last thing...
i feel like we've gotten no update on this or other potential characters being added
They've confirmed future characters beyond Goat, as well, due to having publisher backing. So you can look forward to that, as well.