bhomburg

As far as upgrades on AA go, especially on this route, unless you make it to Executive Platinum and acquire SWUs (four roundtrips to SCL per year) - , upgrading to business will cost you 50,000 miles plus a $700 co-pay each way (because Asia to North America and North America to deep South America will be treated as two upgrade awards, each priced at 25k miles plus a $350 co-pay).
And that is if the upgrade clears. The HKG-DFW flight is notoriously difficult to get an upgrade from Economy to business even for EXPs using SWUs who are ahead of Platinums using miles on the upgrade priority list - there's a giant thread over at the AA forum discussing this - read for some insight.

Airberlin will do retroactive credit for new members - BUT: For new members, miles are credited for flights taken up to three months before registering for topbonus. So that may or may not work for your November dates, depending on when you applied for topbonus membership.

I would leverage the AB status you have now - you will get lounge access and are able to select MCE seats on those AA flights for free, which is nice especially on that 16-hour HKG-DFW flight! - and go with AA going forward.
You require two round trips (HKG-DFW-SCL) for Platinum status on AA in a calender year - that should be perfectly doable for you. It also satisfies the four-segments-minimum rule.

Upgrade-wise, Airberlin will only let you use their miles for upgrading AB metal flights (although that may change in the future - I'm hoping to use them on Etihad at some point) and since they have cut all the Asian routes and don't fly to South America the only way you could use them would be for awards on the AA flights - which requires 200,000 miles for a return trip HKG-DFW-SCL in business - AAdvantage would require 170,000 miles for the same trip.
At least V fares on AA earn 100% miles in topbonus....