I hate when this article of Joel's get cited as an argument not to rewrite anything.

> With that thinking we never get Linux (NeoMinix), tmux (NeoScreen), Clang (NeoGCC), WebKit (NeoGecko), Subversion (NeoCVS), or Vim itself (NeoVi/Elvis/Stevie/etc).

-- haberman (https://news.ycombinator.com/item?id=7288033)

Stuff is rewritten all the time. Servo is not replacing all of Firefox, just an experimental project to replace Gecko by a skeleton crew.