From PTS Patch Notes v6.1.1, "Most Undaunted Mask and Shoulder Style Pages now stack to 200."
Why was this done, and why was it limited to ONLY Undaunted pages? Whatever the reason, it should apply to all other style pages. I tested it on PTS, and it does only apply to these Undaunted monster pages.
Just to be clear, this is a GREAT START.
While at it, here are some other stacking recommendations, which would have positive impacts on the player experience:
Make all other style pages and runeboxes similarly stackable to 200.
Make similar glyphs stackable to 200 (this seems technically feasible inasmuch as they already stack in the decon UI).
Make similar undamaged Alliance War siege weaponry stackable.
Make foods/drinks stackable to 200 instead of the current 100.
Make Alliance War repair kits stackable to 200 instead of 100.
Make anything else stackable to 200 that is currently set to 100 (there are lots of weird things like New Life fish that stack to 100).
Personally, I'd be much more inclined to switch between PVE and PVP if things stacked better. These changes would also make it much easier to manage guild banks and dispense rewards. They would also consolidate guild trader transaction history volume, which would improve performance.
Please keep at it and make more stacking improvements!!!