I am not sure they will stay true to their word but this was stated in the website I posted earlier about. I quote -
"Being the last title we’re developing on our in-house engine, the team has an extra motivation, we’re all determined to close an era with a high note, and a game you’ll remember!”states Michele Caletti, Milestone Lead Programmer. "
- What I interpret from this is that they will stop making games on their in-house engine so Yey for us and the future of the franchise. Maybe things are finally looking somewhat up.