I’ve been working on supporting core-only contexts in our OpenGL renderer, but it’s no easy task. Currently, it’s a compile time option only. You have to pass --override SUPPORT_FIXED_FUNCTION=UNDEF to the makepanda command-line. I haven’t tested it on Mac OS X - the Cocoa code may have to be modified to request a GL 3.1 context.
Of course, shaders are required, either the auto-shader generator or custom GLSL shaders. Panda will use a simple GLSL shader for rendering GUI elements and text in absence of a custom shader assignment.