So it looks like the Template doesn't change when you connect a classic site to a new Office 365 group.
In the new SP Admin Center the template still shows as 'Team site (classic experience), even after converting. Am I being impatient and this will change after a bit of a delay or is this planned?
If planned it results in me getting an error when trying to apply a Site Design (Invoke-SPOSiteDesign), as the Design is built for a Modern Team Site, not a classic one. The only way around this I can see is to connect the site collection to a Hub Site so it inherits the look and feel, but this isn't practical in all cases with the 50 hub limit.
Like many customers this is going to be one part of a much bigger strategy to modernise our tenants and we absolutely need the ability to add site designs to these sites to allow us to implement consistent branding.
Just want to add, I really like the fact this is now something we can do and don't want to seem negative, I just need the functionality to be enterprise ready before it becomes GA.