What does "providing an excellent Battlefield 3 experience" post-Battlefield 4 mean? Will be additional DLC? Unlikely. Does it mean there will be more updates? Potentially. Or does it mean they'll just keep servers active for a while? That's probably it.
What they could (read: should) do is open Battlefield 3 up to mod support around the time Battlefield 4 releases. By then all of the Battlefield 3 DLC (including End Game and Aftermath) will have released and sales for BF3 will have dried up. As pointed out in this weekend's Game Ranter Banter, previous games in the series included mod support and it helped Battlefield 1942 immensely. Even now, the user-made DayZ mod has boosted sales for the three-year-old ARMA 2 greatly, and the community can do great things with the Frostbite 2 engine if they could make their own maps, weapons and vehicles for BF3.