I can see how keyword hierarchy as implemented in Classic would be significantly more complicated for end users. Overall I mostly agree with this philosophy.
However, managing my current keyword list is getting rather unwieldy as it mixes multiple key purposes. For example, in the same list I have all the people I have tagged. I also have keywords answering basic questions like: Event/Holiday (Christmas, Thanksgiving, birthdays, Independence day...) or Why (e.g. family reunion, vacation...), tied to specific activity (dinner cruise, helicopter ride, botanical gardens...)
Therefore, it would be awesome if keywords had additional attributes or facets. e.g. filter the keyword list for all keywords associated with events.