There are no new rules about carrying-on powders. Powders are just as acceptable now as they were 6 months ago.
At PHL in November, my backpack got pulled aside for secondary screening. The TSA agent at the monitor told the TSA agent at the end of the conveyor that there was a bottle in my bag. He asked if I had a bottle in my bag and I told him I didn't. He then asked if he could open my backpack, I told him yes, he pulled out a bottle (around 8 ounces) of a prescription medication for my daughter. Keep in mind that this bottle was a professional sample, so there was no prescription label on it, nothing with my daughter's name on it. He showed me the bottle and gave me a stern but still courteous (NOT accusatory) raised eyebrow. I told him there was powder inside, not liquid. He shook it, he heard the powder, and he placed the bottle back into my backpack and zipped it up for me.
And by the way, I used to LOVE powdered formula. Haven't used it in about 3 years, but man was it convenient for any sort of travel, and I'm talking just driving 2 hours to grandma's house, not flying 1000 miles.