I can't answer all of them, but I'll try to address a few things.
First: we can't do anything about the OC thread other than creating a new one, and there's not much of a point to that at this time. The old one is gone and has been for years.
If it's just the OCs you want to download, there's this pack
here. It hasn't been updated for quite a while, though.
If you want to discuss the creation of OCs for the program... hmm... well, I got nothing.
Next, I don't see a reason to remove the house editor. While houses don't have that many options, it's still more comfortable to edit them from within the program. Why throw that away?
As for filters, the program already offers the option to add your own custom filters if you need them.
Finally, you may have better luck finding non-MLP characters in non-MLP sites (although I don't think you'll find them all collected in one place). Good luck with that.