The two airlines had just two mainline planes in common: A319s and A321s.
The US A319s have 12 First Class seats and the AA A319s have just 8 First Class seats. US announced a long-term plan to install new interiors in the pmUS A319s, including MCE.
The AA A321s feature MCE in rows other than exit rows and bulkheads, while the pmUS A321s do not. Parker has not announced any plans to reconfigure the pmUS A321s.