Why procedural and not Object Oriented, not seen procedural being used for many years apart from C.
Commercially speaking. I would go with Java or C#. Doesn't really matter which they both pay well and the skills are interchangeable with other like minded languages such as python, Ruby and JavaScript.
Haskell is worth the time and effort, although it is very academic, some banks use it, although many in Europe and the UK are moving the code base over to F#.
I don't think FOP will be moving at great speeds commercially speaking. But the techniques are definitely making an appearance in the main stay languages. Especially with Multi-Core chip designs and making code run parallel on them.