I think it will be the last DLC because I think they are going to release Halo 5 earlier than expected. I wouldn’t be surprised if it were announced at E3.
Are there any plans to further support Halo 4 after the next title update? -SitriStahl
We intend to support Halo 4 through Matchmaking, events, essential fixes and playlist design for a long time to come - and while there are no announced map packs after Castle releases later this spring, we have some cool ideas about future content and support that we’re tinkering with right now.
-Frank