Future - Purview vs Fabric for governance

Hello and thanks for reaching out.
Purview is the enterprise governance plane; Fabric is the analytics plane. I don't think Fabric will replace Purview as Purview remains the system of record for enterprise-wide governance. Fabric governance features are intentionally scoped to Fabric workloads, whereas Purview governs the entire data estate.
I agree on the metadata concern which is valid. This has been submitted as feedback. There is quite a ton of work being done on Purview as evident on the roadmap here 

https://cdn-dynmedia-1.microsoft.com/is/content/microsoftcorp/microsoft/final/en-us/microsoft-brand/documents/MS-Purview-Data-Governance-Roadmap-detailed.pdf
I believe at end of the day, organizations should work to build enterprise governance in Purview (domains, glossary, policies, lineage, security) and let Fabric consume and honor that governance for analytics.