I've done tons of this...
First place to start is, lets say you have a car. Pull the ECU and open it up. Why? this is to verify exactly which processor and etc is actually being used in the ECU. This is the first step to ECU reverse engineering. Once you have the exact processor that is being used you can then Search for the Specific Chipset documentation which will have all the information you need to know on how to talk to the chip, often times how to rip the info from it in bootmode, how to flash it, and etc.
Why do you need do you need that information from the chip? because that's what you all know as the BIN and thats needed for finding tables and etc.
Often times certain chips are used in numerous models of cars, so you can start cross referencing the chip with other makes and see if some of the work has already been done and someone has a tool already for reading and writing the chip and etc. Sometimes thats half the work. Generally speaking reading and writing is the easy part. The Disassembly of the ROM (table defining, logic learning, and etc) is the hard part and is often times guessing for people with no experience with a particular ROM image. Having DAMOS files and OEM documentation makes all of this so much easier. but those docs are generally hard to get hands on for the regular guys out there. SO most of the table finding and defining is done painfully and longwindedly (yes i know not a word, lol) the manual way using Hex editors and etc. WinOls, is a very common one.
Honestly, its not about big or small companies. its about who is willing to take the time and spend the money to get it working. and decipher everything. Doesn't take a big company to do it. Often times its never the big company that does it. Its a couple of guys in their rooms or garage cracking stuff and selling it to the big companies.
For the B58 people. First things first... Pull the DME, pull a couple from different models and years to see exactly which processor is actually in there. And pulling a couple different ones will help determine if they mainly use the same Processor. Then find the Chipset docs, or see if there is anything out there that already can read and write the DME so you can get the file off of the DME. I have a Ktag Master for that. So if you guys get a couple DME's and see what the processor is. We can see if Ktag supports it. If it does send it over and ill pull the un-encrypted file off of the DME. but first thing first. find out exactly what Processor is in there.