A couple of clients are insisting on the Modern site’s approach for Project and Task management project – here are some additional notes and articles that might be helpful for any consideration.

• Modern Team Sites /Communication site – Every site is a site collection – This a good blog post which talks about the Ignite announcement and why MSFT chose this approach https://joannecklein.com/2017/11/03/sharepoint-site-collection-advantages/
• Modern Team Sites, Communication sites, Groups, Teams connected sites, etc created through the user interface is not visible in the SPO Admin center at the moment
• To link multiple site collections via Top Navigation – Microsoft has come up with “SharePoint Hub Sites” which are still under development – https://products.office.com/en-US/business/office-365-roadmap?filters=%26freeformsearch=sharepoint%20hub%20sites

• Missing features from Modern UI
• Adding List/Library web parts on to the pages in Modern UI(Preview Mode)
• Search Web Parts
• Refiners missing from the Search results page
• Live Tiles

Customization story(Still in development are Site Design/Scripts approaches) features are available to First release customers

• They have also released some features to “First release” customers and I think we can enable our tenants for very specific people to be part of “First release” – here are the steps http://jermsmit.com/enabling-first-release-in-office-365/
• See meetup on this subject (Classic vs modern) https://www.youtube.com/watch?v=t_h9Z5sVBFo&feature=youtu.be

Yes Modern is the future – It still lacks many important features/stability and still not ready for Prime Time to replace Classic in every use case. Here are some recent quote on this from MSFT and a blog on this – https://dev.office.com/blogs/update-on-modern-document-libraries-and-extensiblity

There are no plans to remove classic mode anytime soon.  For more details, see our post on modern extensible at http://dev.office.com/blogs/update-on-modern-document-libraries-and-extensiblity 

classic document library experience available to all customers through a simple opt-out experience, even as we roll the modern experience out globally.