Ghost Recon: Future Soldier was delayed til January, UbiSoft confirmed that the beta would remain exclusive to the Xbox 360, and "early access" would still be coming to Splinter Cell: Conviction owners.
Before PlayStation 3 owners cry foul, when the beta for Future Soldier was announced, at the time, PS3 owners got exclusive beta access to Assassin's Creed: Brotherhood at the same time. Of course, Assassin's Creed: Brotherhood's beta was active a long time ago - in fact, the full game was released last year.
As for PC owners, they'll just have to wait for the release of Future Soldier to experience the multiplayer. There will be no betas available for the platform.