On one hand this is bad, because a proprietary or just new and different OS will do precisely nothing to win back any trust towards Huawei.

IMO, they should partner with Canonical to get linux done right on their devices and be open to the open source community.

That backdoor jibble jabble is getting old... How come we're so sure that Google doesn't include backdoors as well? Or is it the old and tried "better dead than red" philosophy?
As for the topic, it could be something like YunOS or Kai OS, that is, a derivative for the local Chinese market only. Probably to avoid Google tax and make it unnecessary. And cut down on customization and open sourcing. From what I've heard, Chinese manufacturers don't hide their sources and kernels solely because they want us to buy new phones over and over again. They do it to prevent other Chinese from copying their code. It's quite a common thing there.

Probably easier to install backdoors undetected.