I think the changes in general will not really affect the difficulty. For me it will probably affect my loadout, my starting stats, and how tactical I am with my perk choices, but I'll eventually game it because I will figure out how to do so pretty quickly. I do think the fast travel thing is abysmally stupid because that will get old like real fast. The sleep save thing is kinda annoying, but you probably are not more than about five minutes from a usable bed at any point... But casual players won't like it, and there are a lot of them with Beth games. Worse comes to worse, I'm sure if everything is implemented that was teased, that mods will be out pretty soon thereafter to tweak anything anybody finds the least bit annoying.
I am dubious whether they will actually implement all this stuff that was found in the game files, particularly the no FT and the sleep save thing because that will turn a lot of people off... You are going to disable fast travel but also drastically lower the respawn rates of cleared locations. Great! So instead of running back through places you just cleared out to fight the same guys all over again, you run back through the same places you just cleared out to find absolutely nothing! Sweet! Hope you don't get stuck in a rock or fall through the worldspace on the way back to your questgiver.
Also just to mention, the "Adrenaline" perk sounds kind of unnecessary. I mean, I can one shot kill a behemoth as a sneaky sniper character on the highest difficulty level. Then they are just going to make combat deadlier in global values for everyone AND give you this perk which gives you an increasing damage bonus based on your kill count.
Switching back & forth seems to defeat the purpose of anything added by survival mode. I imagine it would reset the needs timers like it did in New Vegas. If you catch a disease I imagine it would just be cleared when you change the setting to Very Hard or whatever the next mode down is.
Doubtful. All Beth games you can change the difficulty setting at any time and their games aren't geared towards punishing you for how you built your character or progressing to the spot you're at (not to be confused with choice and consequences you make within questlines or whatever). Doesn't seem like there's anything to necessitate that kind of locked in choice from the beginning. When it goes live people are going to want to try it out on their current characters, not start a new one. Some people are going to decide they don't care for it.