No it shouldn't be an option. Like someone else has said, mechanics start to break down if you move the numbers too low.
Take it how it is and adapt to it. Stop trying to lobby to get everything changed to suit your needs exactly.
I am amazed at how people are actually reacting negatively. If it should be allowed for 25mans, why not 10? Its not even the same gear as normal.. Flex was designed to allow people to raid whether they had a few people extra, or were a few people short. Mechanics start to break down? thats ridiculous. How so more than if you have 17 people instead of 25 or 8 instead of 10? "Trying to change everything to my needs"? I really dont see how that applies whatsoever, im just asking a logical question, nothing more.