I would like to see an option for installing updates when installing Mint, perhaps in the form of a tick box in the installation menu. I believe Ubuntu 14.04 has this option (I'm not positive, though) and I think that it would be nice to be able to do this in Mint also. If Ubuntu does contain this option, I think that it would not be too hard to include it in Mint.

I remember, back when I used Quiana instead of LMDE, that the installation typically took only 10 minutes, but the updates after installation could take up to 30 minutes or more. If the update process could be optionally combined with the installation process, I would have been willing for the installation to take 40 minutes if it meant that Mint was completely up-to-date. It was perhaps a bit frustrating to have Mint install so quickly, only to have to reboot and install updates for the next half-hour.

EDIT: Perhaps it would be similar to the Update Manager in that it would assign severity levels and let you decide which ones to install. Perhaps it would even give you an opportunity to install additional kernels as well.