The teaser pretty much says it all. I expect that ZENworks 11 SP2 will be the last version of the product to support Primary Servers running on 32-bit Windows or Linux servers. With the ZENworks "Pennsylvania" in 2012 we will be requiring a 64-bit server running a 64-bit platform. This allows us to fully leverage the hardware and further improve scalability of the solution. We will continue to support the ZENworks agent on 32-bit and 64-bit managed devices and satellite servers.
For smaller environments (say just a couple hundred of devices or less) it would be nice to keep 32-bit primaries around since the additional memory of 64-bit Linux isn't needed. At least until such time that the db vendors (especially Sybase as that's what's typically used in smaller environments) require 64-bit.