I would like to know what's the process to sign-up for Office 365 early preview so that I can access the new functionalities such the new SP online modern admin center , Hub sites etc before it's made available for GA . I read somewhere that Microsoft gives the early preview functionality which can be tried out in a test tenant . Please check and let me know.
Also, you may find on occasion you have to switch between Targeted release for entire organization or Targeted release for selected users, as some features only appear for a while in one or the other. When this happens it is usually mentioned in the relating blog announcement. You can set up a free dev tenant, this is what I use for this purpose, this for up to 5 users for a year.
The new SharePoint admin center is an example of something that was previewed with a signup form and you had to apply but it's coming to Targeted release very soon now, from next week in fact. No announcements yet on how hub sites will be released, that I have seen at least.
Basically there are Microsoft Office 365 Program Previews that are announced from time to time and you can request to be part of them...bad news here are that there is not a central source of information where you can check what programs are available to join