TCO on the server is great and all, but where's the workstation?
Great TCO on a server is one thing. Where's the fully compatible, if a bit slower, $200 impulse buy desktop? Where's the $400 low-end laptop? Where is the $3000 professional workstation version? One of the reasons x86_64 is a server hit is because code for it can be banged together and sanity tested on any number of other, cheaper systems. The final performance tweaks might need access to actual server hardware.
With lots of development in Python, Java, Clojure, Perl, Ruby, et al being a Linux box is nearly sufficient. Even then, though, if there's no C or C++ library to call from those languages then you'll be porting those libs or coding around them, and spending a bunch on programmer salaries in the process. If IBM wants to make IBM great the way IBM previously made IBM great, they need to intentionally do what they did accidentally the first time: align a desktop architecture with what they want to sell in entry-to-mid tier racked servers.