MOTM

I would make it three modules.  

An Input module with the really high quality mic preamp with phantom 
power, obviously a gain control and the bicolor LED indicator.  I 
would also include a guitar/line level input preamp as well.  I 
would use a second clip indicator for this as we're not all guitar 
players and may want to process a signal from somewhere else without 
clipping.  I would also include a phase reversal switch.  I would 
only put one mic pre and one guitar/pre per module.  For those who 
want stereo they can buy two.  I would use an XLR for the mic input 
and a TRS for the guitar/line level input.

An output module with 2 channels of output with 2 balanced line 
outputs for each channel.  I would use TRS jacks not XLRs anyone who 
needs XLRs could just make a special cable or the stooges could sell 
them.  Obviously an output level control.  I would also put the 
headphone amp in this module with two outputs and a level control.  
Anyone who wants quad could buy two.

The envelope follower module with all your tricks and speaking of 
tricks if you really want to be tricky make it a pitch follower as 
well.

I'll take two of each!!!