It does no harm to keep him on NFI as opposed to get releasing him.
He has had 2 16 game healthy seasons now, he is not ancient, he is what 28 or 29, so by that he has a good 2 to 3 years left at least.
If he is on the roster, you need to have 6 inactives anyway, he would just be an inactive until he is ready to play.
He doesn't have a lot of mileage on him as people think.
Jackson is not ready yet, he needs to learn NFL pass protections better. He has not done anything, that we seen anyway, to make himself stand out to be kept over DMC. I do like what little he has shown, as for his speed, quickness. But unless he just wowed the coaches in practice. Which I have not seen in many reports. IMO, he is still PS bound.