Forestry its NOT an addon. To qualify as a Addon it would need to "Depend" on a father mod of sorts (Like how advanced machines can NOT work without IC2). Forestry its a Mod of its own that doesn't need Buildcraft to do anything (Although its quite recommended to be installed too).
Besides i remember reading that eloraam was planing a AutoCrafter after she releases the computer blocks and she just did. (Theres also that "RedPrint" that im not quite sure what its going to be used for)
For the other "Additional Pipes" addons, apart from the teleport pipes and anything liquid and power related, Redpower Tubes can do many of those and you don't need to craft a different type of pipes, and hey the pipe system just keeps getting bigger and bigger with more machines that provides a lot of good uses.