I don't think it will be - and to be honest, I suspect that throwing yet another engine into the mess that is the MCC, will only make things even less stable.
But I'd absolutely love it to be added. With the addition of ODST, we've sort of dropped the pretence of it being a purely Chief-focused collection - and of course, you could always make the argument that since he does technically appear at the very end, if you use the camera trick, Reach should be included anyway. For all I have a lot of criticisms of Reach, particularly multiplayer, the campaign was generally pretty strong, and firefight was excellent. To be honest, the firefight alone would be enough to get me to buy a current-gen version of it, since I always really enjoyed it.
Plus, I'd love to see it at proper, modern graphical fidelity. While I appreciate the art style a bit better now, Reach always felt like quite an ugly game, and due to the combination of that hideous motion blur and low framerate, plus the low resolution and poor antialiasing, even going back to it now it still isn't a pretty game. Getting it integrated into the MCC with the motion blur off, the framerate and resolution raised to modern standards, and maybe even a few of the subtle lighting tweaks we got with Halo 3, would really help beautify the game. Given the high quality of its texture and polygon work, too, it might even feel like a natural part of the current generation, as the engine for the most part has also held up fairly well.