[FWIW, My original reply to the post:]
Hello ______:
Thanks very much for the suggested clarification. Your message has been posted anonymously on the Poker TDA Forum in the category "Suggestions for New Rules and Amendments" at the following link:
http://www.pokertda.com/forum/index.php?topic=790.0.
I would note that your question involves an all-in situation which is addressed in Rule 11 (Face Up for All-Ins), not Rule 12 which addresses non all-in showdowns. In your all-in situation both of the remaining hands (the all-in and the caller) should be turned face up at once since all betting action is finished for the hand. Don't wait until all remaining board cards are dealt out.
Nonetheless, your point that there could be some uncertainty about what is meant by the "final betting round" in Rule 12 is important. What is intended is the last possible betting round before the showdown (i.e.: the river in THE or 7th street in 7-stud),
regardless of whether actual bets are made or not on that round. [if bets are made on that final round, then it's the last aggressive action who may be required to show first if the players don't spontaneously table their cards... if no bets are made on that round, then it's the 1st player to the left of the dealer button.]
Thanks alot for the question and suggestion!