I'm afraid the next Nexus will also have no MicroSD slot... Google has said that when the current Nexus was released.
They don't want it in their future Nexus devices. (as also seen on the Nexus 7)
This is the newest rumor as of now. There will be three nexus devices, The Optimus Nexus from LG, the Xperia Nexus from Sony, and the Galaxy Nexus II from Samsung:
Last rumor I read, besides some of the info above, is that the next Nexus would be called "Superior" and it'd be a "small upgrade" over the gnex. Same display, 1.5Ghz dual core A9, upgraded cameras, and a sd card slot. Rumors are rumors and I'm hoping this one is wrong. I don't care too much, though, as I'm pretty sure my gnex will keep me happy until the 2013 Nexus/Nexii. I just want "it" to do well for Google/Android.