Thank you for taking the time to post your findings.
> Is the ColdFire v1 JM128 part actively supported by freescale?
Sort by date-order on the "Tools" tab on this page shows recent updates:
Flexis 32-bit V1 ColdFire USB Microcontroller|Freescale
Last Documentation updates were in 2012 and 2013.
> Who would I talk to about getting a bug fix released for the JM128 USB Bootloader example (AN3748)?
Try your local Rep. They have better channels back to Freescale than you can get here. Getting Documentation Updates is hard. I've been asking for some simple fixes for years (since 2010 for bugs going back to 2000) with no results whatsoever. Although the quoted response I got is amusing, it is also heartbreaking:
Re: PIT hw boo-boo. Read if you need accurate PIT (CF)
the redaction doesn’t seems to implies that writing the
same value to the PRE bits doesn't reset the timer.
Otherwise the best place for Customer Support for known bugs is probably this Forum. Google can find it (or that may be that Google knows I like this place, so it may only work for me). Post details of your changes here. You could even attach your OS X program here.
I suggest you also read:
USB bootloader for Codewarrior doesn't work with Windows 8.1
Tom