We are currently considering whether we should change from Drupal to Processwire at least with some sites. It is quite important desicion for us, since we have about 30 websites from very small to few quite big ones. I have heard and seen lots of good things, but not having an in place editor is a bad thing.
Most of our users are not professional web editors. In our old system we had quick link to editing on backend visible to users browsing web with enough rights and this helped a lot much like in pw. But still I think for an modern cms you shoud have option to use in place editor.
Having it as module preferably including default/example theme working with it out of the box might be a good solution. Versioning would be good, but it is not necessity for us.