Just noticed this lonely question.
I've swaped a few LMM's into other stuff like boats where BCM fed factory dash setup isn't an option. We typically use marine MFD from companies like Garmin to display engine gauges.
Biggest issue is HS GMLAN isn't an openly known CANbus protocol, so nobody makes a digital plun-N-play dash to work with it. Yes there is some OBDII based stuff out there, but you'll be spinning 4k with the tach reading 2400r due to network traffic delays associated with OBDII.
To convert raw HS GMLAN engine/trans data into something usable by off the shelf digital displays, I designed a little PCB gateway few years back that translates directly from HS GMLAN to whatever language the display speaks. This approach removes the gauge lag, and also allows data logging without disconnecting the main gauges. Opens up some cool stepper motor gauge options I really like using. See attached
Another option is Lingenfelter make a box that converts HS GMLAN data into voltage output lines, to drive old school analog gauges.
That's what's out there I know of so far.