Nintendo and Retro need to have a sit down because clearly something there is wrong, either in how Nintendo is managing them or how Retro goes about working.
5 years with not even a single game to show for it is unacceptable, if Star Fox Racing next existed than what on earth have they been doing for 5 years. Presumably Nintendo's been paying their salaries for 5 years.
Retro is a good developer obviously but only 5 games released in basically 20 years of operation is very poor.
If SFGP never existed that doesn't mean they don't have a game nearing release. People need to stop making that weird leap.
Based on job listings, LinkedIn info and all of that we can guess they were working on at least two projects, one of which likely started some time in 2016. It's extremely possible that this project is done or close to done and will be releasing in 2019 or 2020. They can have a small team including QA working on that while they begin full development of MP4.