Additional Slot in <wa-page>

[quetwo]

I know the already has a ton of slots, but one common view I'm dealing with is a CRUD view where you have a navigation to the left, then a list of records, then the detail view in the main area of the page (with an index of fields to the right of that)

I know I can accomplish it with a grid or something similar, but it would be nice to be able to have that use-case taken into account.
This is a similar setup that you would see for an email client, messaging client or something where you drill into data deeper as you move to the right.