From the latest Unity Keynote we can discover some stuff for URP and HDRP only, so…
Built-in has been the “legacy” render pipeline for years already, there will be no future developments for it.
And yet it’s still the user preferred render pipeline…
Classic Unity.
I found this notice that still shows some development for Built-in RP as well as for UGUI: https://portal.productboard.com/unity/1-unity-platform-rendering-visual-effects/c/50-ui-integration-with-shader-graph?utm_medium=social&utm_source=portal_share
My guess would be that it wasn’t much trouble to support built-in so they decided ‘why not’.
But to parrot what atmoicjoe and indeed Unity themselves has said - Built-In has no future. Unfortunately I also have to parrot atomicjoe and point out that Built-In is still best of the three when it comes to a blend of feature-completion, platform support, and stability… for now anyway.
SRP is definitely meant to replace Built-in entirely, but I think they are being careful not deprecate Built-in until it becomes unpopular among users. Unity Tech probably have some analytics from developers to see how many projects are using Built-in vs SRP and they’re waiting until the usage drops down to a certain percentage.
one of the unity developers wrote recently
would be good to have some info early,
that when its getting deprecated/removed?
saw this warning message in webgpu thread,

thanks, good rendergraph info there!
didn’t notice any mentions about possible deprecation timelines though?
devs said that they would give some time for the new system, I think until the next LTS cycle (usually a year)