I suspect the real story here is likely finding a good target (SFRP2), more so than the microbubbles. Finding a specific enough target always seems to be the limiting factor in immunotherapy, nanoparticle-based drug delivery, GNP-based radiothermal therapy, etc.
Now if they could find a good target for more cancers (I definitely agree on breast as a good target--elastography ultrasound is already a big topic of interest there), it could have a nice impact on treatment options. Since you can't really image too frequently by MRI, CT, etc. due to exposure limits, you can't do high-frequency watchful waiting, which biases clinicians and patients towards intervention when they detect something.
In breast cancer, this is a pretty hot topic: all these frequent / early mammograms are detecting lots of DCIS, and the standard thing to do is lumpectomy. But there's growing evidence that these are likely being overtreated, and many if left alone would likely not progress to invasive carcinoma for a long time. But since there's no great way to know on a patient-by-patient basis, and since you can't really keep a close eye on them by frequent imaging, it's tough to do otherwise.
But if you could image the breast cancer really well by ultrasound, you could do such a watchful waiting: image frequently, and so long as there's no change, keep monitoring. (Not sure if this would have have the resolution to detect an in situ cancer like DCIS, though. Will have to read the article.) It would be nice to see such watchful waiting options open up for other cancers where treatment choices are perhaps otherwise unclear.
I've also seen early work attempting to use interference patterns in ultrasound (putting a few piezoelectric membranes at the right spacing, etc.) to induce apoptosis at specific spots. It would be interesting to see if this work could help enhance that