'the rationale that they are actively evaluating other develoment platforms?
"However, now that Ladybird has forked and become its own independent project, all constraints previously imposed by SerenityOS are no longer in effect. We are actively evaluating a number of alternatives and will be adding a mature successor language to the project in the near future. This process is already quite far along, and prototypes exist in multiple languages."
They need to commit to not using C/C++ for the majority of the project.
If not, then yes it can’t be taken seriously.
Unlike existing browsers?
Existing browsers have an existing codebase to deal with.