Pre-orders for Battlefield: Hardline are already available on sites like Amazon and Origin for either the standard edition ($59.99 USD) or the deluxe edition ($69.99). Even with these pre-orders, DICE is quick to note that they will continue to support their still broken Battlefield 4 title.

DICE outlines what they are continuing to work on for Battlefield 4 in their latest Battlefield blog update.
Continued Support: There are dedicated BF4 teams in Stockholm, Uppsala and LA that will continue to address any issues that might occur. But more importantly will also look to make significant additions to the game.

Netcode Patch: We are also working on a major update to the Battlefield 4 netcode.

Community Test EnvironmentMore Features: Other features rolled out recently such as Squad Join, Rent-A-Server and Loadout Presets, many which have been directly requested by you in the community. This trend will continue.

Now, I'm not in the CTE for Battlefield 4 but I am hearing some good things about the improved tickrate and a few other changes. It's a bit late in the life of the game, all things considered, but it's nice that improvements are still coming to the game. It's also a good thing since it seems Battlefield 4's continued troubles seem to already be hindering Battlefield: Hardline hype.