It looks that layout and template are confused here. I already described this in another thread Apply Template to an Existing Object - #123 by java
Basically relationships can be included in both: layout and object contents. Notion includes properties (relationships) into layout and does not allow inclusion in the contents (or template). Template predefines object contents, but not layout. It seems that Tana does it similarly. Maybe it calls it differently, but this is really a layout, not template. Template defines a custom document-style contents. While layout defines how relationships are rendered on the object canvas and where the contents goes as a box.
How AnyType could do this.
So every object has a type and a list of relationships. Some of these relationships are included in object’s type and some are not. For every object type you can add a new type-specific layout. Similarly Notion has a custom layout per database! AnyType can do it per type. You can name it maybe “Full” or “Custom” or “Type”. By default it should display all relationships defined in the object type, and then include all other relationships with display option “display if not empty”. Please check how Notion supports this: it is really nice and illustrative. When user adds a new custom relationship to an object of a given type, and this relationship is missing in the type, then you can automatically add this relationship to the layout with option “display is not empty”. But user can override it to “never display”.
This would match Notion and also support AnyType specifics of allowing custom relationships missing in the object’s type (not possible in Notion).
AnyType also allows to include relationships in the object contents (you can also call it object’s body or document — I am not sure). This contents is regulated by a template. But we don’t really need it to match Tana/Capacities/Notion. We rather need powerful layouts. Templates are also needed, but their use cases are a bit different and their role can be heavily revised as you build powerful layouts.