Always save standard values rendering field as a delta of its base template rendering field
By default, Sitecore doesn't support rendering inheritance for templates standard value items.
Scenario: TemplateA has a standard values items with presentation details defined ("__renderings" field defined). I create a templateB inheriting templateA. By default, templateB "__renderings" field is empty, so its inheriting templateA rendering. If I change templateB presentation details, Sitecore copies templateA "__rendetings" field value, apply changes to it, and saves the result in templateB "__renderings" field. By doing so, Sitecore is breaking the rendering inheritance. From now on, any change to templateA presentation details won't be reflected in templateB.
A simple solution exists and is already used at some levels in Sitecore. It is named layout deltas. If Sitecore would save a layout delta in the templateB "__renderings" field, it wouldn't break the rendering inheritance.
There are a couple of blog posts with workarounds to get the desired behavior. Here's an example: https://www.cognifide.com/our-blogs/sitecore/complex-layouts-in-sitecore-using-standard-values-hierarchy/
It would be very nice if Sitecore would use layout deltas out of the box.
Ivan Lieckens commented
Have a look at Sitecore.XA.Foundation.Presentation.EventHandlers.LayoutInheritance, I believe this covers your requirement...
Jean-Francois L'Heureux commented
In fact, layout deltas should also be used for normal items "__renderings" field to avoid breaking rendering inheritance with their template.