This will help cut down on items circulating in pipes more than necessary. Comparitor can be used to detect full inventory and send redstone signal back to the extractor which turns it off.

Nifty, but perhaps a more general solution would be better.
I'd like a block that pipes connect to and items pass through. Redstone power blocks items from passing through, and low levels of power just slow them down. Now you have a way to block extraction, slow the stream of items based on feedback, or construct elaborate mixers/combiners following whatever logic you can build.

Relationship between red stone and pipe is very difficult, and I need to contemplate. There is also a way to add an attachment such as Redstone receiver, so it may be related to #30.

What about a block with an inventory that refuses to accept items based on a redstone input, as opposed to redstone-pipe interaction?

Do you mean to add blocks like buffers? But I think we can do it by only setting the hopper between the pipes.