Modern subsites?

I am concerned about what happens to existing structure in this scenario. I understand that splitting things out into site collections can be better in some instances, but what about where you have different solutions or sub departments and you want a separate group associated with it for each? Or the case where you have regional sites and then departments per site that need to re-use content from the regional site collection root (site columns, content types, etc.) Are we expected to duplicate all those columns across the site collections that need them?? To rule the possibility of O365 Group Enabled subsites out completely is going to hamper existing tenants switching over to the modern experience in a major way.