I typed up a large response here to a few posts then forgot to post it and closed the browser, so I'll cut this one short out of frustration.
Not everyone will agree with our choices, not every ship excites every user. We do plan on including the new Charon class frigate. I think of it like the Lightening fighter planes. The first iteration of the Rebellion release will be a barebones update from the Entrenchment release with only the required changes. After that we'll begin iterating the timeline of the game to post Halo 4, including the addition of new Charons and the UNSC Infinity.
We are not doing loyalist/rebel factions in Rebellion. However, we will be doing some complicated changes to research, wherein someone will basically choose from the new UNSC or the old, meaning more expensive, but shielded ships versus large numbers of less powerful ships. The Infinity will not be the only titan. More info to come on this at a later time, so no questions please. The other ships seen in Halo 4 will likely not make it into the game, but may if we decide we have time to dick with them and come up with good reasons to include them gameplay-wise.