No, there is currently no support for this. We have, however, been thinking of this and added most of the stuff needed to implement this, but we just had to skip this, as well as a few other things, to get the release out. Hopefully we can add this to an UI upgrade in a not to far future.
Are there any (un-)official workarounds? This is one of those things that really improves on the content-managment experience.
There are no easy work arounds for this. You can replace the entire page tree either through configuration or code in an initialization module but then you would have to create another page tree which would do this. It's possible to do this by inheriting from our page tree but it's probably some work to get it going so unless you have the need for it right now I'd wait to see if we manage to get this in to the first add-on upgrade of the CMS UI.
so a year after, still no icons ?
can it be done in the new episerver 7.5 ?
Support was added for this in the 7.5 release:
There is examples for this (container page) in both the Web Forms and MVC template packages for 7.5.
Is it possible to have custom icons for page types in the content tree? There were some hacks for this in EpiServer 6 but I was hoping there would be official support in 7.