Since no one else has answered, I'll venture that the problem is a manpower issue. I don't think the team still has the devs necessary to address the dangling ends. They have some devs but maybe not enough or not the right devs for the job.
I know we always say this. But what Illysia said covers 100% of the problems we have in developing PS.
Let me try and answer your questions as best I can.
Mastery changing/reseting - Currently this only effects magic but according to the dev team it will grow to involve combat skills and crafting as well. We have worked hard to reach full potential in many different skills and to have all but 1 or 2 skills in each category limited by an end-game system that, in all honestly, looks like a slightly reworked class system is a real slap in the face.
It is somewhat like a class system, but only as much as picking a Way to become a master in is. I don't know the details to get into it, but you will have the ability to pick to be a master in a skill which will improve what you can do.
Weapon Balancing - This applies to all weapons. Looted weapons were balanced so you can potential get one that is better than the current best crafted weapon. Not a bad idea in my honest opinion but the changes to the chance to loot good names in general have been reduced to an abysmal low. I don't want to know how many hours it would take to loot something that is even comparable to crafted gear. Looting aside, what about two handed weapons? Their damage per delay ratio is always worse than duel wielding two one handed weapons and they have no noticable damage reduction or block advantage or rating on them. On the opposite side of the spectrum daggers have a fixed delay that cannot be modified by either enchanting or looted names.
Progress on this is sporadic and patchy mainly down to only eonwind being able to do it, combined with the fact the whole combat system is crazy complex with many things influencing many other things, like loot rate, lots of things effect the loot you players see. There are a number of things being made by rules, and adjustments to combat balancing are perdiocially one of them.
Shindrocks Crater - This project has some serious excitement building but it seems to have fallen off the face of Yliakum.
The main problem here is that the primary Dev running it is no longer active, and the other dev who worked on it is now busy expanding the basis for special attacks and assocaited quests. And no one else has the time or motivation to pick it up right now. So like many other projects within the dev team (much like RPs in game) once the main drive for doing it is no longer around, progress stops. It will likely be picked up again at some point once the todo list for the active devs is much lower.
Laanx Mind/Wrath Weapons - This fix was expected at least 4 months ago in a mini update but seems to be being delayed and coming in a different mini update with other stuff?
It might be obvious to you what this is, but I don't think anyone has mentioned a bug with these weapons to me in some time. Assuming it has been fixed, which it sounds like it has from what you said. Best guess is that the fix was missed off the things to update during the last update. Each update is only a selected list of things, so when something gets missed off it can't be in the update. I've missed loads of things off update lists in the past, but they mainly break the server so it gets noticed during the update and then updated

Quivers - Not essential but given the insane amount of arrows it takes to kill stuff we are really missing it. I almost think a weight and size reduction is also in order for arrows or a accuracy buff for bows. Seems at the moment ps is bent on making ranged weaponry very inferior to that of close quarters.
Well, unfortunatly, adding quivers won't happen any time soon. For a number of reasons, lack of artist, lack of coders, inability to make new mac clients which makes a full client update impossible. It does sound like another instance of a need for combat balancing could improve the situation, something that eonwind would need to comment on for a full answer.
Mastery Wands and Gear - These were worked on probably over a year ago now and I've not heard anything of them. I have wondered if this is due to the magic system being delayed until weapons catch up for I don't see the point in this when close quarter melee weapons when combined with magic buffs/debuffs have always been top dog when it comes to spike and sustained damage regardless of pvp or pve.
I don't know what you mean by 'Mastery Wands and Gear', perhaps you can explain what you mean.
I believe that the majority of our problems comes from the large amounts of loose ends that are left dangling. Has this content been aborted? Is it being developed for the Unreal Engine 4 client? Is there even an Unreal client or what is exactly meant by "A working demo"? There are so many questions and concerns for the furture of ps but there is so little information to be found.
The number of lose ends is down to small number of devs and there being too many things to all get done at once. There is no content being made specifically for an unreal client, as we have no idea when that will happen and until we have some sort of time table there isn't any point. "A working demo" is being able to log into an unreal server version of PS and run about the maps, thats it. But, we only have one dev, ravna, working on it and only when they have time to work on it. So its going to be some time off still before its ready.
I hope this is somewhat useful.
Venalan.