Had the same issue. The problem was caused by my antivirus/internet security.
I stopped the antivirus/internet security, started the game and BattlEye was installed corectly, after that I could restart my antivirus again. After that it worked like before. (No need to repeat it on every start)

Hope this helps.

AFAIK devs already confirmed something like this (called "world containers").

According to the timeline in the review of 2014 it's planed for the second quarter of 2015:
https://dayz.com/blog/a-year-in-review-2014-for-dayz

But to work this needs the inventory system to be reworked:
https://twitter.com/eugenharton/status/590113933631029248

I'm uncertain about it:
On the one hand I think that covering yourself in zombie guts or rolling around in a mass grave to camouflage yourself wouldn't fit dayz because the infected are simply infected humans (no super-human senses) and because of that they shouldn't be able to distinguish between players and infected by smell.
BUT on the other I think it would be nice if you'd be able to deceive the infected by imitating their appearance and behaviour. E.g. by having a "walk like an infected"-animation, wearing dirty, ruined stuff and no weapon like you suggested.
(But the range should be limited; if you get to close the infected should recognize you nevertheless)
In the end this could enhance PVP as well because you could deceive other players as well. (E.g. you could evade a sniper by pretending to be an infected because the sniper doesn't want to spend all the ammo on all the infected in the area just because one of then MAY be another player)

I like the idea for the same reasons you mentioned. But I think it would be a bit too easy if you could grab all the apples on a tree at once in no time.
(As a solution the apples could appear one after another, with a pause of like 10 sec)

Beside the fact that a humanity system would be unrealistic like nexdemise stated, you pointed out the main problem of such a system: "Every system can be circumvented somehow".
But if you can't trust the system, it doesn't gain you anything; it doesn't give you any additional information because every player you come by might know how to circumvent the system and kill you even if he is flagged as hero/friendly/etc.
In the end it wouldn't change anything.
And like nexdemise pointed out, such a system could mistakenly punish someone for selfdefence.

IMHO another system could help to "replace" the humanity system:
The often requested introduction of beards:
The longer you live, the longer your beard(and/or hair?) grows.
If someone has a long beard, he might be either really lucky or he might be very cautious and KOS. Or he might tend to be friendly but cautious and if you don't approach him he might ignore you.
If someone has no or only a short beard he was recently killed and might be just unlucky or he could tend to deathmatch around the cities and you should shoot first.

You would need to interpret the information, but this system couldn't be circumvented.

I think in the end a (non-ideal) humanity system would give you more of a false sense of security than real security.

The mod had a similar system (humanity-system with hero/neutral/bandit-classification), but it diddn't work. There where to many ways to circumvent it:
E.g. one member of a group of bandits became a hero by playing accordingly for a while and then acted as a bait for unsuspecting survivors for the rest of the group.
After a short while nobody trusted the system anymore and the distrust between the players grew even more.

@Loffas: At least one of your wishes should be satisfied soon (if I haven't misinterpreted the infos):

"There is also progress on cooking in the built-in fireplaces which I hope will breathe life into these sad and abandoned houses."
(source: http://dayz.com/blog/status-report-02-jun-2015)

(I think, if you can cook on these fireplaces, they should warm you too)

Added the feedback "Blur dark areas to decrease the advantages of cranking up gamma and give the night a more natural look" (http://feedback.dayzgame.com/view.php?id=1294) which could be a possible solution.