I'd prefer to play on Survival with the ability to save the game whenever I want
Meaning, exactly the point H4-I3 made above "All the neat new features of survival without having to sleep to save."
I could also imagine wanting to turn off "Disable Fast Travel" from time to time, but given I generally like to play without it I'd be keen to try it with that enabled too. For that one, I'd be keen to try it both ways.
The rest of the "survival features" . . . based on what I'm hearing, I'd always want those, and wish they were in the game now. My last FO3 install was heavily modded with the mods that added these types of "realism" features, also my Skyrim install.
Now that I think about it though, I wouldn't have a problem with a "require sleep to save" features in survival IF portable bed rolls were a thing . . . its just the silly idea that: "I must get back to a bed so that I can save this game and turn it off, even though I've only got 5 minutes till I need to leave for my hot date/important appointment . . ." etc. that I don't like.
. . . end of the day . . . we users are legion and we have probably near infinite numbers of personal preferences. As such, game options panels that provide users with more "plug-n-play" and user friendly customizability (meaning 'get the effects of mods but with the simplicity of a toggle switch) seems to me to be a good general design strategy.
If there really is a large enough portion of the user base who want to be required to sleep in order to save, and get special trophies for playing that way and such, then I'd suggest an additional "difficulty tier" above "Survival" called "Masochist!"