I guess I'm one of the few that would rather see AA with a strategic advantage of having its own connection to TBIT. Opening the T4-T5 tunnel allows seamless operations for DL/Skyteam between T5-TBIT. I'll deal with the shuttle bus if it preserves this advantage for AA/OW.
The only reason For opening the tunnel is if AA is finally going to exercise their options for any gates in T6.