It sounds like you are really asking: "When Horizon introduces a new plane (kit, arf, etc.) can we get a model of it for Real Flight?" Which, to date, has never happened, except as part of an upgrade package....
"Never" means pretty much "when it was distributed by Great Planes and/or Knife Edge Software was independent".
When Horizon took over distribution after buying Great Planes, their aircraft only came as part of an upgrade.
Knife Edge has now been owned fully by Horizon for only a couple of months. So we'll just have to wait and see if that changes. It would be a nice co-marketing thing to drive sales- "buy the Whiz-Bang kit, and get a free download for Real Flight included" or "Download it for Real Flight, and get $10 off the kit".
But they have a lot of work before that, probably, to fix up really serious stuff, like the DX9 problem....