I flew to and from Japan with my Brompton in May/June of this year - mo packaging at all, gate checked both ways from SFO to Narita, no problem! I did take the hinge locking clamps off though (I was afraid they'd come loose).

I tried to repeat the same trick flying from SFO to Portland in August - no go at all. SFO has tightened restrictions at security - they wouldn't even let me enter the line. They had one of those stands showing maximum carryon size, and the Brompton definitely exceeds it. I pointed out that many people in the line had bags that were way over this size, and that they were only picking on us because our bikes were obviously different. They still wouldn't let us enter, though to be fair I noticed afterwards that they also turned away people with ridiculous rolling luggage

Ended up having to pay $25 per Brompton to check as normal luggage (covered only in slip cover).