At this point my hope for height advantage/disadvantage is that they make it modable.
It's interesting that you focus on that aspect when height advantage is a rules as written implementation of advantage.
Pg. 173 of the Player's Handbook:
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You usually gain advantage or disadvantage through the use of special abilities, actions, or spells. Inspiration (see chapter 4) can also give a character advantage on checks related to the character's personality, ideals, or bonds. The DM can also decide that circumstances influence a roll in one direction or the other and grant advantage or impose disadvantage as a result.
Our DM, Larian, has chosen to grant advantage for positioning, per the rules.
That particular rule can be used to justify almost anything giving advantage or disadvantage - the same could be said if they'd implemented a rule that halflings get advantage all day every Tuesday. So it in no way says anything about whether a particular home brew rule is good or bad, and what a lot of people are arguing is that that particular home brew rule is a bad idea and overpowered.
Except it's not a homebrew rule. It's 100% D&D 5e Rules as Written.
Larian, our DM, is choosing to reward tactical positioning.
Although your Halfling on Tuesday suggestion is an interesting implementation of Lucky.
Technically, that is a rule Allowing homebrew advantage, saying the DM reserves the right to grant it as they see fit, to homebrew it in amongst the already written instances. Regardless, the core issue of that is that allowing any instance of highground or being behind an opponent is proving to be overpowered and unfun for the game, so many players have asked for it to be changed to a more flat bonus with some wanting it removed altogether. Yes, larian is our DM, and Yes that rule says the DM can grant advantage, but that doesn't change that the DM adding something in is considered homebrew. The DMG and PHB are filled with instances of "The DM can change this," and that itself is a repeated confirmation that the DM can homebrew, can make changes, house rules. And this house rule is not working well for the players, so most DMs would change it.
