There's a lot of refactoring to do in Gecko's graphics stack to fit the new rendering model. While they do that, they can also accelerate one thing at a time with WebRender, testing incrementally. Things like SVG which WebRender doesn't have yet, can also use the old system and be included in WebRender as images.
The old system will still be needed post-WebRender for printing at the very least.
> The old system will still be needed post-WebRender for printing at the very least.
Isn't it possible to take a frame from WebRender and print that? Having two separate systems seems like allot of unnecessary maintenance. Especially if one of those systems is only used on rare occasions like printing.
The old system will still be needed post-WebRender for printing at the very least.