Writing kernel modules in Haskell

First, the 10x figure is bogus at best.
Second, 1/10th the development time, at the cost of losing control would be OK for a one off number crunching app, but it's not an option for an OS Kernel.
Finally, if you care so much about rapid development, then maybe C++ is not your best option. Go with Python (I have read there are wonderful math libraries) or something like that.
That coming from somebody that has been writing C++ code for the last 14 years.
My biggest gripe with C++ is that it's like a ubercomplex laser scalpel: great in the right hands, deadly in the the wrong ones. It's a great language for top-down communication (for example, writing libraries), but sucks for interchange of code among peers.