The idea of Big Team Battles not being a part of Halo 5 at launch wasn't a popular call from 343 despite its protests that Warzone was an evolutionary replacement for the mode. As a result it now said it would be working on BTB for post-launch content including new maps tailor made for the mode and a playlist. (And don't forget: all of Halo 5's maps are free.)
@deepvoice_ming Warzone is the evolution of BTB, on steroids. We'll also be adding a more traditional BTB mode post-launch.August 18, 2015
Multiplayer designer Quinn DelHoyo has said in an interview that "Big Team Battle will have its own [matchmaking] playlist when it launches". More importantly he's added that "we’re crafting all new maps that are designed from the ground up to cater to Big Team Battle. These will include a healthy mix of infantry and vehicular combat that Big Team Battle is known for." That latter part does sound a lot like they've taken fan feedback on board and decided to bring BTB back in a more substantial way.
Seen something newsworthy? Tell us!