It was not rehearsed extensively. However it was worked on during the first leg with the thought that it could be a part of the European stadium tour setlist rotation. It was the full band version. Never transpired obviously. U2 has a lot of great ideas and some poor ones as well when they "tinker" with stuff in soundcheck. I would say there are a TON of songs that are very unlikely. But I would never say never on just about anything that has made an album.
The "Popcore" was actually being worked on for the tentatively planned for use on the N. American Vertigo stadium leg for the summer of 2006. When that was cancelled rehearsal of the Popcore, specifically Mofo, stopped. Although they began working on Velvet Dress prior to the MSG shows occurring. I do not know if they had thoughts of using it for those.
Someone else pointed it out, but did anyone realistically expect U2 to play An Cat Dubh ever again? Not many, if any. So you never know.