Netlist can now be included as sub-circuits. That's the same approach SPICE uses. 
The implementation also supports nesting. 
Opamp emulation now is as easy as

    /* Opamp wired as impedance changer */
    SUBMODEL(op, opamp)

    NET_C(op.GND, GND)
    NET_C(op.PLUS, clk)
    NET_C(op.MINUS, op.OUT)

The missing bit now is a central submodel repository. I'll start a discussion soon on the list.

nl_examples/opamp.c is an example of a impedance changer stage followed by a 1:2 amplifier stage.
System size (= number of voltage levels to be calculated) is between 20 - 30.
Using a simple, yet better opamp model than usually implemented in the old discrete core, I get

./nltool -f nl_examples/opamp.c -t 30
startup time ==> 0.002
runnning ...
30.000000 seconds emulation took 0.438599 real time ==> 6839.96%

Which leaves quite some buffer to emulate even complex mixing and filtering stages in real-time :-)
Fix MT5440 [Alex Jackson]