So, a good number have seen the interactive guide showing off what the game has to offer multiplayer-wise(If you haven’t, CLICK HERE!!!). If some old gametypes may not be here officially, I think they can still come back through other means through possible clever use in Forge, and Custom game settings.
1-Bomb Assault
We may need to use Dominion’s base capturing method. Maybe in the settings, the round will end, and have the base instantly supply itself with explosives that will detonate, violently killing everyone inside!!!
Race
In Reach, we could forge a mongoose to become an objective, where staying on it will count as points. In Griffball, the ball can be used to score points.
What if it is possible to forge the mongoose, and set the goals as checkpoints, and set a 1-way shield door to keep players from just running back and forth? 
Classic CTF[/B}
Ok. Maybe not ENTIRELY, but the idea is kind of the same.
We could use the Griffball settings to allow custom loadouts, or restrict the loadouts to pre-set conditions. Then restrict the ball to allow the opposite team to touch the “Flag-Ball”.
Even though we may not be able to keep the “flag” from being tossed like a ball, I think this could be the closest we could get to classic CTF.
This is just a small list that I can only come up with in my mind. However, the main idea is to convert a gametype to play as another. Such as how Flood was originally a custom slayer gametype, and Griffball was a custom Assault gametype.
Maybe this isn’t the whole list, maybe it it. However, they may not be entirely gone. What do you guys think?