This should only affect those who are using the SliverFillViewport widget or RenderSliverFillViewport directly.
# Why deprecating RenderSliverFillViewport?
Currently RenderSliverFillViewport has a few bugs in its implementation, such as https://github.com/flutter/flutter/issues/23873
. With the introduction of SliverLayoutBuilder, the functionality of RenderSliverFillViewport can be perfectly replicated at the widget level, without those bugs.
Instead of continuing to maintain RenderSliverFillViewport, deprecating it in favor of SliverLayoutBuilder seems to be more appealing, as SliverLayoutBuilder is more generic, composable and it is a widget.
# Migration Path
Mostly like no migration will be needed for code that's not using `RenderSliverFillViewport` directly.
If you're using `RenderSliverFillViewport`, consider replacing it with a SliverLayoutBuilder at the widget level.