The grace period is short based on the requirements of the software publishers. It was originally only for those who accidentally registered the wrong iLok. Now that there is lots of ownership and rights issues, many publisher want to be able to know how to support their users. With iLoks moving all over the place, it is hard for them to do that. The grace period often causes more support than you would think.
Some vendors also require their approval to remove and iLok, even during the grace period.
The rental market and those with larger accounts is something we are considering. It is easy to do technically. The issue is unification of the policies of 80+ vendors to agree.