My greater point was that exchange rates tend to be self regulating (in this situation), you'd expect it to return to mean rather than get stuck in a feed back loop. This is China though so I have no idea how much they need to heed economic reality.
Once the 7 line is crossed, owners are more likely to seek diversification through getting out of CNY and into USD/Gold.
Some of that downward pressure on the FX is likely good for demand in China (hence Trump saying they are doing it competitively) but it's also bad for liquidity in China (to the degree people start to price in further devaluations and capital flight kicks up again).
That's the balancing act the PBOC is trying to manage.
Thusfar they've done a pretty good job balancing, though it remains to be seen how the end game looks.