Hi everyone,
Thanks so much for all the feedback! Overwhelming but very valuable and on point! 
There are many questions around our plans for high-definition and what is long term vision for HDRP and URP.
While we are kicking off more practically this journey towards one render pipeline, we don’t expect you to change from one day to another if it does not make sense for you.
But one of this year’s practical milestone of this journey is actually to enable getting high-definition graphics to more players (internally we are romantically calling it “Build once, beautiful everywhere” 
):
-HDRP users will be able to bring their high-definition games to portable consoles players.
-URP users should be able to push the visual fidelity of their games on all platforms. We cannot get it all at once, so we will be especially focusing first on games and applications with dynamic content where baking is not possible (in game editor, destruction, time of day, dynamic lighting, city builders, simulations,…). URP is already capable of creating beautiful content, but dynamic lighting is a fundamental piece which has been behind and this is the biggest current gap we have identified talking with a lot of you.
Next/Long term, our vision is to continue to push fidelity/performance (eg: shadow caching, shadows quality, volumetric fog,…) focusing on URP, while we maintain HDRP as long as necessary.
As many of you mentioned, just merging HDRP into URP would be very dangerous and probably not what most users want. We need to be cautious and take the time to push what URP is capable of while respecting what makes the identity of Unity: cross platform, extensibility/customizability, ease of use, small build size, fast iterations. This is why HDRP maintenance is important, and why we are not deprecating it.
Regarding migration path, we have not mentioned it because again we are not deprecating HDRP and not asking HDRP users to move to URP. However, with physical light units, volume based physical sky and pre and auto exposure integration in URP, it should be much simpler in the future to share a scene between URP and HDRP, or port from HDRP to URP. With the already common Render Graph backend, HDRP’s custom passes and URP’s custom renderer features share common interfaces. And Shader Graph shaders and VFX Graph effects are already mostly compatible with both pipelines. This post gives an overview of what can be and cannot be shared today between render pipelines, and how the URP evolution we are working will make it even easier.
While we are cautious, we are confident in this path because we have relentlessly been investing in the past few years on unifying the pipelines. With already many common modern foundations like DX12/Vulkan/Metal, SRP Core, SRP Batcher+RSUV, GPU resident drawer, Render Graph, Shader Graph, and VFX Graph, all available today, a unified upscaling framework coming soon and common physical light units and pre exposure backend “tomorrow”, the porosity between URP and HDRP should allow convergence in a gradual way, while continuously pushing what you will be able to achieve and benefiting all.