Signing up of Office 365 early preview

Not exactly, what you can do is setup Targeted release (First release) - https://support.office.com/en-us/article/Set-up-the-Standard-or-Targeted-release-options-in-Office-365-3b3adfa4-1777-4ff0-b606-fb8732101f47.  This will get you access to features earlier but not everything. 

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 https://social.technet.microsoft.com/wiki/contents/articles/37830.office-365-how-to-set-up-a-free-developer-tenant.aspx, 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.