I am currently preparing to switch to DITA. The learning curve is steeper at the beginning, but I find the overall concept of topic-oriented, information-typed authoring with content reuse very attractive.

Some people might say that writing in XML is annoying, but it isn't if you have a decent XML editor. In my case, it is Emacs nXML mode. Customisation is possible with DITA-OT [1] and plugins, and yes, it is also based on XSLT. Overall, I think DITA is an industry-proven XML powerhouse. It may be boring, but it has huge potential for anyone with advanced documentation requirements.

[0] https://dita-lang.org/dita/archspec/base/introduction-to-dit...

[1] https://www.dita-ot.org/