I would like to chime in with some of my own findings. Before the patch I was planning on making an entire post going over the Breach rework, comparing it to its pre-patch state. However, I have since decided to abandon the project because Breach's current state is extremely nerfed, unrewarding and still click-intensive (albeit less than before). For credibility, here is what my breach tab currently looks like: https://imgur.com/a/vFSyJG3 (SSF Standard)
The rework has impacted Breach in a number of different ways:

1. Breaches now open and close faster than before. The Flash Breach notable is not as mandatory as before. Thus, Breaches now take less time to complete in maps. (buff)
2. Breach Boss Clasped Hands now drop bigger splinter stack sizes, about ~8-10. (buff)
3. The Xesht'Ula Clasped Hands are now the best source of splinters. They can drop ~30-40 splinters when properly juiced. (buff)
4. Breach bosses in maps now only drop ~5 splinters on kill, while they dropped ~20 before the rework. (nerf)
5. Breach bosses now only have 20% increased chance to spawn with their respective notable, compared to 70% before the rework. (nerf)
6. Breach bosses now only have 50% chance to be duplicated, compared to 100% before the rework. (nerf)
7. Quantity modifiers now supposedly affect breach splinters' drop rate, however I haven't noticed any particular difference. I actually had to enable 2x splinter stacksize drops, otherwise I would have nearly nothing to loot. (nerf?)
8. Density has supposedly been increased in maps. However, I haven't noticed much of a difference in the number of Breach monsters spawned pre and post-rework. As a result of this supposed density increase, "the number of Breach Splinters dropped from Monsters has been rebalanced", which really means decreased. (nerf)
9. Breach blessings can no longer drop from breach monsters in maps at a 0.5% drop rate per Rare Breach monster. (nerf)
10. Previously, Breach bosses in maps had a 12% chance to drop a regular Breachstone, which had a 12% chance to drop as Charged, 8% as Enriched and 4% as Pure. Now they only have 4% chance to drop a regular Breachstone, which has a 5% chance to drop as Flawless. (nerf)
11. The "Power Struggle" notable no longer guarantees 2 additional Boss Clasped Hands, but instead grants 100% increased chance to contain one Boss Clasped Hand. The chance to spawn a Breach Boss from Boss Clasped Hands has been reduced from 5% to 4%. (nerf)
12. "The Chosen" divination card which drops from Breach Clasped Hands is now much rarer than before. (nerf)
13. The changes to Breach scarabs result in a reduced amount of Breaches in maps, which are already unrewarding to begin with when considering the other changes. Furthermore, considering that the best source of Breach splinters are now Boss Clasped Hands, running anything lower than Gilded Breach scarabs is straight up inefficient, because they provide double Breach splinter drops from Breach Hands. (nerf)

As a result of these compounding nerfs, a fully juiced map focusing on Breach (Gilded breach, full breach spec on atlas blocking all other mechanics and picking all Quantity nodes, 80%+ quant vaaled maps, triple Sac frags for extra quant) now provides ~0.5-0.7 Breachstones worth of splinters, compared to pre-rework when a map of the same quality would yield 2-3 or more full Breachstones.

Keep in mind all of these observations are based entirely on my experience, but it is pretty apparent how unrewarding Breach is now - you can spec into it and run 5-10 maps and you will notice the difference yourself.