The original reason for the track-width rule change was to support an easily verifiable way for tech to confirm compliance with track width limitations.
As it stood, the example cited was at an event, three different measurements of the same car resulted in three different numbers and no repeatable way to get the same number twice.
Tech must have a high-enough percentage of accurate repeatability for verification of compliance.
The suggestion was to do away with absolute measurements (the ideal solution provided close to 100% accurate measurement every time) and instead focus on the marked wheel offset (which can still be measured accurately 'in the field' should a wheel manufacturer get sneaky) plus any spacers installed (and to verify they were the same on each side of the single axle) to determine "track width compliance".
That's all this was and no spurious underlying reason for changing it other than a wheel manufacturer marketing a wheel as being "track width compliant" when it was a +24 offset (which had previously been thought to be "non-compliant").
I, for one, don't see any reason to pull the letter as this makes for a simple method for any home-based entrant to verify their track width.
Stock subframe, control arms, uprights, wheel offset of X, any spaces? BAM! Track width is compliant!
Guess I'll be writing a letter in support of the now-pulled letter (if that's possible).