There are reasons SE keep the update notes hidden until after the patch. There are ways to exploit the system if you know beforehand what they are going to fix. Other MMO's have learned the hard way by giving out too much information.
Anyways...why does it matter if you know beforehand? What are you going to do with the information besides say "oh...they are going to fix that". Where is the actual benefit?
Just think of it like an X-mas present. May be socks...but it may also be a new BB gun you've been wanting.
That's not necessarily true. Blizzard keeps a running set of patch notes up for the PTR that outlines most of the upcoming changes at any given time. Sometimes to the PTR changes don't make it live and sometimes some of the changes that go live weren't on the list, but the majority of changes are available for all to see even before the patch date is announced.
I've noticed that SE has fixed several bugs and issues without listing them in patch notes, and they've also stealth nerfed things already, too. The bug fixes were appreciated...can't always say the stealth nerfs are.
The way I see it, SE is creating a game with rules that govern how things work and they're not very good at informing the playerbase when they change the rules. Sometimes it makes no real difference, like the bug that used to activate DoH abilities that were left on your character when you switched to a DoL class. Ahh, the mirth of going to take a swing at a mining node and all of a sudden your character activates Maker's Muse. It never really bothered me but at least now if my character activates something while mining, it's usually actually useful.
Other things like nerfing success rates and outcomes of Standard and Rapid synthesis can be very costly and frustrating things to change without informing your players. Let's not **** around here...most people don't even read the patch notes anyways. And since SE isn't making use of the launcher as a tool to list such things without having to go out of your way to look for them, the number of people who read the noees would be even less than you might expect relative to other MMOs where patch notes are prominently displayed when you log in. Nevertheless, it's frustrating as a player when you notice that something has obviously changed, the changes are causing you to be unsuccessful at something that was previously not an issue, and the resulting failures carry consequences. In the case of crafting, blowing up several dozens shards + mats in the process of learning that SE has changed things without a word can make a person lose faith in the developer.
I've noticed some changes that seem helpful but any time I find myself observing a helpful change that hasn't been announced in patch notes, I can't help but wonder if it's really an intentional change or a new bug as a result of something else they changed that I shouldn't be exploiting. One such change is the ability to use Guard to raise your shield while you're in the middle of casting a spell. Is it working as intended and a boon to casters who find their shield arm falling just as they've started a 3 second cast, or a bug? Don't know, because SE has been making all kinds of tweaks and adjustments without saying much about them.