Here is my current need.
I have several jobs configured in Hudson.
Some of them must be run sequentially, some others could be parallelized.

Currently due to the sequential needs of some jobs, I must define only ONE
executor. To resolved that I had to install another Hudson's instance. It is
not clean at all.

One useful enhancement is to associate some jobs to a specific executor.
If an executor is defined for a job, that job will run only on that executor.
If no executor is defined, the job will run on any executor.