Yup. I got yunohost.org running on a free instance on Oracle cloud (using a PaYG account) but costing nothing. - Ive then spun up an Email, Frendica server (limited to users on my domain) and Takahe to try out ActivityPub.
I think that a killer app for activityPub would be if MSFT or Google offered it as a service on Workplace / Office365 . (I mean Id rather not use either of them myself)
Many Open source alternatives exist already such as vTiger and CiviCRM.
For my two cents worth I think they could do well by integrating with Nextcloud and Drupal or WordPress (Or whatever comes out of its current shambles).
From the article it seems like they are creating a extendible object model which in some ways is similar to what SharePoint has with its lists. Nextcloud has an add-on (Tables) that is a proto version of this. CiviCRM has worked to integrate website data collection from Drupal / Wordpress well.
Thinking from front of house (website) to back of house (CRM) then Nextcloud the missing link is to Nextcloud ( So documents and images can flow forward into the website Media Library ) and the extensible object model for data.amd being able to link unstructured data (documents etc. to structured data. (Not an expert on CiviCRM so not sure how flexible it is. )
But good on them for having a go. Let many flowers bloom. Even if it doesn’t take off some of their ideas might get adopted by someone else in some other way.