On a side note, I don't mean to be the bearer of bad news but I think you need a better plan than this, cairo has been in various states of inactivity and deep maintenance mode over the last several years, if anything more backends will be removed, not added. Also, cairo is an immediate mode-style renderer following the PDF imaging model made for print -- it's fundamentally the wrong approach for high performance rendering. You may not see much improvement even if it did have a Vulkan backend.
