I think you have to ask yourself this. What is the goal of this capital gains exemption? Is it to provide tax-free savings for farmers to retire, or is it to actually assist, in theory, selling your land cheaper to your children, for the next generation of farmers coming in? If it's the latter, if you want to look at increasing it, you may want to just think outside the box and say that if you're actually selling it to a younger farmer or someone in your family coming in, maybe there could be a higher exemption, versus just selling it to a neighbour who's going to be a larger farmer.
You may want to look at how we can use that system to accomplish what it is. What's the goal, I guess?