It feels like problem with these aren't the ideas, rather the "let's just" approach/expectation in front of them.
For instance "Let's just add an API." I think the approach to an API as "just" a feature to your product will be about as successful as saying "let's just add a UI". To implement a successful UI one needs to be thoughtful, thorough, and bring in people who specialize in it. Why should any other interface for your product be any different? It's not that it's a bad, or good, idea, rather one that shouldn't "just" be done.
For instance "Let's just add an API." I think the approach to an API as "just" a feature to your product will be about as successful as saying "let's just add a UI". To implement a successful UI one needs to be thoughtful, thorough, and bring in people who specialize in it. Why should any other interface for your product be any different? It's not that it's a bad, or good, idea, rather one that shouldn't "just" be done.