IMO - making Eve more safe is not a good idea in w-space nor anywhere else in the game. POSes are not safe and the POS replacement should not be safe either. If you put your assets into your Citadel, they should be very vulnerable. If you want the advantages, you have to put something on the line and it isn't just the cost of the structure, it's the cost of everything you've chosen to store inside. This serves the dual purpose of giving players a strong incentive to defend their assets.
It does not make sense to introduce more safety to the game. Clearly people are willing to risk their most expensive assets in POses as it is right now. Players don't need any incentive to use Citadels. If the benefits aren't worth the risk, people shouldn't use them.
Vulnerability and Reinforcement
With regards to vulnerability windows, I think it's a poor design choice. CCP has listened too much to whiners who want to control the safety of their structures. POSes, as they stand right now, can be attacked any time of day. Citadels, as announced, can only be attacked during certain windows and you won't even know when that is unless you're on grid when it happens. This is a problem for two reasons:
1. In k-space, you can easily go back and check a Citadel every day, multiple times per day. The system is static and can easily be accessed. In w-space, you can't. You have to dedicate an alt to sit in there for a week to figure out when their vulnerability window is.
2. Vulnerability windows don't make much sense. I would rather have more control over when your Citadel comes out of reinforcement (so if you're attacked in your non-main TZ you have the opportunity to defend in your strong TZ). People should be able to attack you whenever they want.
My next issue is with regards to how long the reinforcement period lasts. As it stands, reinforcement can easily last for a week or longer. This simply will not work for w-space. A w-space siege (that is contested by the residents) currently can take a full weekend to pull off (Friday through Sunday). It is necessary to have 24/7 control over all of the wormholes leading in and out to have a successful siege take place. Part of the reason we can get this done is because the reinforcement timers are 24-36 hours - not multiple days. Yes, it's boring, but at least you can dedicate one weekend to it and be finished.
The Citadel system can be manipulated to drag out your reinforcement over many days or even a week. It is not feasible to maintain control over a wormhole system for that long as people will simply not skip work/ school for a whole week to maintain 24/7 hole control, and if you don't maintain hole control then the defender simply can resupply and get pilots back into the system (something that isn't possible if podded out with hole control). This might make more sense in k-space where borders are always constant and you can always find your way back, but it does not work for w-space.
Finally, our new Citadels have these lovely guns and such on them - but they don't automatically respond to hostile targets on grid? This is silly. One of the nice things about a POS is that a lone or unorganized attacker is thwarted by the presence of guns and ewar on my POS. I can be down the chain and my POS will shoo away the annoying troll trying to shoot my POS for fun. (Obviously, a serious attacker could handle what my POS could throw at him.)
With the proposed system, Citadels won't actively defend themselves. Instead, you'll have to have someone manually gun the defenses. This means that choosing to leave my Citadel and go down the chain somewhere actually means I'm leaving my Citadel open to attack. What does that mean? During my vulnerability window, if I leave my Citadel I need to ensure that either someone or someone's alt is left behind to man the guns and watch out for attackers. This is not fun game play.
In fact, this is nonsensical. My behemoth of a Citadel should be smart enough to defend itself from hostiles on grid, just like POSes do. A single pilot trying to troll us and entosis our Citadel should be blapped by the Citadel. An organized group of people should be able to withstand the guns (by using logi, etc) and entosis our Citadel.
I have no problem if an organized group comes along while I'm not there and is able to tank my Citadel's guns while entosising. I do have a problem if a lone guy in a frigate can start a whole reinforcement cycle while my friends and I are doing some PvP down the chain somewhere. Come on, CCP.
Additionally, the aggressiveness of your Citadel (or other structure) should be tweakable. If you want a freeport or live in high sec, you probably don't want your Citadel blapping every neutral who lands on grid. If you're in w-space (or anywhere else) and you don't want neutrals near your Citadel, it should defend against them.
I like the overall idea of these new structures. I can see them standing in as a replacement for stations in the long run and I will be excited to see industrialists opening up market stations where anyone and everyone is free to dock.
I do think, however, that CCP needs to take a long hard look at whether or not their designs fit in with the culture that is EVE. To be blunt, making things safer is a poor direction to take. Citadels and other structures need to be high risk, high reward.