I just built a box out of Ender IO reinforced obsidian with a 3x1 hole in the side facing me. I manually spawn and kill them. After 60+ kills, I have not had an escape. After seeing the Direwolf20 video where they nuked Fireballs base, I noticed Killer Joes and Tesseracts did not blow up. So that should mean the wither can't hurt them either. A couple killer Joes with Etheral swords, fed nutrient via tesseract should hold up to the initial blast for automation, plus killer joe collects XP. I just can't see a need to automate them fully. They just aren't needed for enough things. Even if you want them for power, it only takes a few minutes to get a bunch, which will make a stupid amount of power. By the point you are ready to deal with Withers, most people have a good power gen setup already.
I enjoy automating some things, but others I just like to do manually. I found too much automation gets me to a point where my world no longer needs me.