> Maintenance timesink might easily outweigh the gain in development time.

That is correct. However, in Haskell you need a lot of discipline to guide a big project in the right direction. Maintenance can quickly became a nightmare due to very dense code.

If maintenance is the main issue I would choose Ada than Haskell. I have no problem to understand my own Ada code written 10 years ago, even without documentation. In Haskell however I had problems to understand my own code which was just some weeks old :-)