I'm pretty excited about the hype around a 
metrics layer.
At Airtasker, We are actively investing in this layer, which allows our organisation to easily define, use and discover metrics.
It makes sure that metrics are the same in our BI tool, SQL engines (and experimentation tooling? 🤷♂️)
Some examples of active development are 
dbt metrics and 
transform.
It would be amazing if GrowthBook can facilitate for those types of data sources in the future. 💪