http://press.jal.co.jp/en/release/201010/001659.html
British Airways completes oneworld co-location at Tokyo Narita
At Terminal 2, British Airways will offer its premium customers access to JAL’s lounges. Its First Class and Executive Club Gold tier members will be able to use JAL’s First Class Lounge, while its Club World and Executive Club Silver tier cardholders will be offered JAL’s Sakura Lounge.
Expect Sakura lounge to be even more crowded

Last few times I was there, the dinning area was really crowded and I could hardly find a seat. Not the mention about the shower wait time will now be even worse