Unless you’ve heard, John is the guy that wrote the characters for Wrex, Garrus and Javik from the first trilogy. These are the best characters throughout the trilogy and definitely a fan-favourite. On top of that, the lad was responsible for the superb Genophage plot in Mass Effect 3. As such, John deserves to be in the team for Mass Effect 4.
On the other hand, the fans are also worried that John might be transferred to another project. After all, Bioware is a mega-corporation and getting transferred is a common practice.
All in all, Mass Effect 4 success will be a certainty if John Dombrow is part of the team. If not, then the fans will be gutted and scrutinized with what Mass Effect 4 is going to offer.