What features would you love to have that would be unfeasible to build yourself?
One that comes to mind is broken link tracker w/ keyword search. So if Zed's Open Source 3D Engine link is on my page & still working, but the keyword "Zed" no longer appears on that site because Zed was bought out by MiracleSoft, then I want to know about that ASAP because I partially represent Zed's amazing work, but would be happy to find and post some alternatives since I don't want to represent MiracleSoft.
More simplistic but I suppose the same idea stands, that if you update your twitter.com/sue-soap to twitter.com/sue-newley-wed but forget to update it on your personal website your should get a "alert" that it's gone out of sync.
The reason is I love working on CSS stuff, but writing the HTML part is too tedious for the amount of pages I want to write.
Examples: https://pandoc.org/demos.html
You can style the output using the --css flag: https://pandoc.org/MANUAL.html#option--css
Useful features are the ability to show and easily update a list of events for performances or exhibitions, and media for portfolio or headshots etc.
Then again, rather than owning the solution, the service could spot that you don't have the relevant best practices in place and provide instructions on how to fix it (e.g. pre-populated DNS entries).