Yeah that makes sense, and would certainly be doable. A long time ago I wrote a prototype of clientside callbacks that could be embedded within the layout, check out the examples in Dash Clientside Transformations by chriddyp · Pull Request #142 · plotly/dash-renderer · GitHub. It was a really cool idea but we decided to scrap it because we felt that learning it was “too different” than regular callbacks. We wanted an easier interface to switch from regular callbacks to clientside callbacks. But maybe it’s time to bring back that old PR back…
Yeah I could see how this could get messy. Do you have a simple example use case of this? It might be easier to work through some alternative API design ideas with a simple code example.