You can submit any feature requests to https://servicestack.net/ideas with a lot more details on each feature request.
But a lot of these sounds like UX preferences which are unlikely to be considered unless there’s a lot of demand for it, e.g. I’ve no desire to over complicate it with a different way to edit data, esp. as we need the full screen real estate to show contextual validation errors.
You can see examples of how related data is handled here, i.e. you can navigate to the related data table, it doesn’t show it inline:
Why would you need to multi select rows? You can only choose a single row to edit at a time.
But honestly I don’t see much on that page which I consider a good fit for Locode which is a RAD tool which auto generates its UI driven by the metadata of your Services, we support some declarative customizations but it’s never going to have the level of customizations of a developer control like their Table grid which requires a lot of bespoke code for each of their examples. Locode doesn’t do bespoke code with hard coded columns, it needs to be auto driven.