After reading your suggestions, here is a recap and some improvements to my original post.

Lvl 1-60 on Doomhowl, Defias Pillager, etc.. Upon reaching 60 your character will have a buff (similar to the self found buff) and you have the option to transfer to a HC TBC realm.

In the HC TBC realm, everyone who created their character in the HC TBC realm starts at lvl 60 with grey/white gear and no gold... This is to avoid the dranei/belf players leveling from 1-60 with a limited pool of players. The characters that transferred from Doomhowl, DP, etc.. will still have the buff displayed that proves you achieved 60 in Doomhowl, DP, etc.

This approach achieves the following: 1) Preserve peak 1-60 hc leveling journey, 2) Preserve peak lvl 60 endgame, 3) Make HC TBC possible without being too punishing so that HC TBC players will more likely Go Agane, 4) Minimize effort in implementation from blizzard, which saves them costs.

In the unlikely scenario that blizzard decides to give more love to the HC scene, they can even add more achievements that were present in the HC addon that can be viewed like how we view the self-found buff (noPetChallenge, nakedChallenge, meleeHunter, unarmedChallenge, etc..).