This would probably really come into play with older stuff that has RailSounds 2.5 and wireless tethers, you can pretty much drop-in the ERR RS Commander by just adding the serial data buffer into the mix. I do hasten to add, for the upgrade above I had a source of 5VDC available for the serial port buffer. I believe the AD-20A (stand-alone) that is used with RS 2.5 also has a 5VDC output, still looking at that.
If I understand what you're doing correctly, I have two comments to add to the discussion.
1) Your use case of RailSounds 2.5 plus wireless tether is exactly two locomotives. Not exactly a big market to target, I wouldn't think.
2) The stand-alone AD20 receives its +5VDC from the RS2.5, so you'll need to add a source for it when you remove the RS2.5 board.