If we're talking about 2-way horn systems with 12" or 15" drivers ... vertical spacing between drivers does become an issue. Lower crossover points do become more attractive in these applications for home HiFi use.
I don't think the comments about 'crossovers can go anywhere' were referring to a specific crossover for a specific application.
I think they meant, that there is no more problem putting a crossover in any one particular frequency range, than in any other particular frequency range, with no specific speaker design in mind.
Iow, comments were not about a crossover for any specific design, but about crossover ranges to avoid in general, no matter what the speaker design.
I do not think such frequency ranges to avoid exist.
For example, folks often say to avoid xovers in the 2-4khz range where the ear is most sensitive.
Ime, crossovers work just fine in that region,
if properly implemented.
So, in this described contest....yes, crossovers can go anywhere, no problem