We need to separate this:

• link to the local page where one exists and no linking if none exists
• link to some placeholder page

The latter needs a lot more conceptual work. It's going too much into implementation already.

I also don't think we should use a new parser function here but instead add a parameter to the existing property parser function.

Ok, question: Why do we need this when we have T99897: {{#property}} parser function should output EntityIdValues as local wiki links, once we have article placeholders?

Closing this as I don't think we should have a separate parser function for this. Instead I'd rather change the current one. We'll need to get community input about how much that will break.