Metaphysics is one of the broadest branches in philosophy, with questions about the nature of the world, with sub-branches within it such as ontology, epistemology and more.
I'd like to ask a question that's sort of meta-metaphysical. Metaphysics is usually (if not always) speculative: idealism-materialism, God, origin of the universe, space-time, and more subjects of interest to metaphysics which are almost always taken as speculative ideas, with outlash against it being too speculative and not connected to reality (ironic), or worse - that it doesn't have any real results or it can't ever be tested, and more comments like these.
I've heard here (from @Conifold) that metaphysics might be considered as an incubator for scientific theories, which is interesting take on it (especially when, to my knowledge, this wasn't how metaphysics was treated most of the history of philosophy), but could be helpful for the question - assuming this is true and metaphysics is an incubator for scientific theories, when does the metaphysical analysis "enough" to be taken into "action"- incorporated into a scientific theory? Is it just something that's always out there, a blend of ideas waiting to be brought to science?
In other words (though it's an entirely different take on the question) - does metaphysical analysis justifies itself on its own, or is it always to be considered as a starting point for science? And if it is really only a starting point, why would we have philosophers that'd explore metaphysics on its own and not only let scientists approach it when needed to their theories (if it isn't already the case, I'm not sure about that, but we still got philosophers like Thomas Nagel who is first and foremost a philosopher, and he talks about metaphysics)? And this, in other words, means - is metaphysics as a philosophical branch (and I'm talking practically, in the Academia) dead, and only approached from within science departments? (Note that this paragraph talks about a different topic, but a topic that's derived from the questions from the previous paragraph.)
When talking about metaphysics here, I mean metaphysics in relation to science, obviously not the metaphysics that talk about art, politics, etc.