This is a never ending story.
Feelpp should be revisited regularly to enforce clean code:

• use recent features supported by compiler and Feel++, currently C++17 Cleanup using C++17 features #1408
• make sure the code is readable
• make sure the code is not only readable but also changeable
• the code should be elegant and efficient
• make sure cmake process is working properly and support third parties
  • petsc
  • boost

This is an epic, it will stay open. We will attach however attach issues related to the principles above if they apply.