How to manage a PDE function that does not want to commit to any dates, ever, but also does not want to uncouple release from launch?

One tactic that I like to employ when I dont have buy-in yet from XFN partners is to pilot something with no cost to the other team. My guess is that your stakeholders dont yet grok the value youre proposing. So in this instance, dont force your stakeholders to adhere to your launch plan. But create one anyway and measure its effectiveness.

So let your team ship items when ready, but in parallel create a marketing moment for after launch. Then measure key metrics -- leads generated, product trials, customer counts, active usage, etc. and if you can showcase that when you create a marketing moment you can drive more product value to the organization, then you can start leading the conversation around the business impact created/lost by not committing to dates and becoming a more mature product development function.