Oh well, if that happens I hope I can at least go out with a bang.
Hopes' words being "story doesn't allow for the harem" has always been ambiguous and open to interpretations.
It's either gonna be;
A) MC is given an ultimatum by the ladies to pick one of them and stop fucking around,
or
B) At least one or more of the LIs die due to story and it becomes impossible to achieve a "complete" harem.
Given Hopes initial plan for Luna was her being not accepting MC being with other girls, but that being now unlikely (from Hopes' reaction to it when I asked about it before), I think it will most likely be B (i.e. someone dies).
If that's the case, I think I have an idea who will likely meet the tragic fate, but damn that would be really devastating.