One such feature I would like to see a return in Fallout 4 would be an improved Hardcore Mode from New Vegas.
The system would delve deep into the essentials, I.e several meters to monitor your sleep rate, fluid intake, and starvation, as well as adding weight to your ammo and making Stimpaks less effective.
The mode could also improve on like the "Super Hardcore Mode" mod developed by Obsidian's Chris Avellone (Who also worked on Fallout 1 and 2).
Obviously, for anyone that doesn't know, this feature would be optional.
Link Provided to the Mod Description:
http://www.ign.com/boards/threads/new-super-hardcore-mode-mod-released-for-new-vegas-by-obsidian-itself.250006429/
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I have a feeling they will add it in. I remember going through the hardcore mode in NV, finishing it while not getting the achievement. Them I realized I already did the hardcore setting on my first play through. Never the less, it was still fun. The toughest part imo was the ammo weight addition, especially when strength was not leveled steadily. [spoiler]I will not divulge the hours invested in FO/ES[/spoiler]