My version of hard mode is simple: no subjob. (Use a mule.) Get to 95 solo (the exception being G1 before the recent patch, which I duoed with a level 55). Actually level 80 is enough. Solo all the missions you can along the way. Note that you will probably need more than one job, as some of them can't even reach their G5 solo. Protip: not too many jobs work well solo without a subjob.
Campaign battle and GoV alliances are allowed for exp. Mailing stuff from your main is allowed. Abyssea solo-only before 80 or higher. (I held out until 93 to prove to myself just how hard Aby is solo starting with no cruor or atma. I recommend it. Just try getting 10K cruor, especially without quests. I never even had 2K cruor.)
Medium mode: no subjob as a group with friends. Bonus if you go static such that you ding levels at the same time as much as possible.
How about this... Raise and reraise still works, but home pointing does not. You die without reraise, you have one hour to get lucky and get a raise from a kind stranger passing by, or frantically beg everyone on your friend's list to come rescue your ass because you have 15 minutes left.
I think people would
be a lot more diligent about reraise disconnect then try to get someone to raise them in that case.