I would be surprised if they have the expertise and manpower to do that.
They are mostly relying on LineageOS now and putting their own cloud, microG, and App Store app and branding on top of Lineage. Even now they are not able to roll out Android releases and WebView updates timely. Them maintaining an AOSP fork would probably end up in an outdated, broken mess.
My money is on GrapheneOS and maybe LineageOS to do it when needed.
I agree, nevertheless, Murena has 50 employees and is profitable as a company. Idk how much money lineage and Graphene have, hopefully the partnership with Motorola is going to provide them some funding.