Hardcore CTF needs to make a return for the following reasons! Now this may be a bias view as I was a through and through hardcore fan on BO. However in the list of reason you may find some points that you agree with (hopefully all of them).
Hardcore CTF offered call of duty a fully structured game type, much like S&D is but allowed you to respawn. It offered players an objective to go after. The rounds were long enough for all the players on both teams to rack up some nice kill scores, use their kill streak rewards etc. No one was running round aimlessly, everyone new where they had to be and what they had to do, which meant there were some pretty interesting gun fights and tense games, as it forced you to find a way to break through the opposing team.
The second point on structure is the team. Hardcore CTF accommodated every single type of player on call of duty. You had your runners and gunners up the front mainly going for the flag, you had your campers playing a defensive role and then you had your more tactical players moving slowly up the maps playing more of a mid role helping to get the flag and blocking for the flag runners. You could play what ever style you wanted to!
Second Point is
No matter what style you chose to play, it forced you to work as a team! Great for a group of mates that are playing together, great for jumping on and socialising with people you've never played with before. Again, a point that I have already made, teams were most of the time pretty evenly matched due to the HC CTF following which lead to some great intense games, gun battles, 1 on 1's, defence vs front players and all round good competition!
Third and final point
Not realism in the sense of graphics or gun shooting. Realism as relative to real life. HC CTF offered players games they can relate to off the xbox. This was a huge factor in playing HC CTF! It was a game of two halts, and some times a decider, much like football match or a paintball game. I would reference american sports but they are all played in quarters! If you lost the first half, you had a second chance to pull the game back win the round and take it to overtime. You felt like you were actually playing to WIN! not just running round shooting whatever moves. This is definitely something that MW3 is missing.
Now I shouldn't have to say this but I will. CTF is on MW3 but only in core mode and the round times are cut down. It's over before a decent back and forth game has started. The reason people play HC is because of the 1 shot 1 kill (more realistic) makes you focus more and makes the games more interesting and less frustrating than having to pump a full clip into some one. There are plenty of threads on here about which is better core or HC so I won't go on about that. I fully understand the arguments that not everyone can be catered for, but I am coming from the view point that HC players have got a bad deal on this game (I understand that there may be less of us than core players) but we are still paying customers and deserve our say and opinions. I believe that HC CTF with the BO rules and structure was a big part of the HC community. And this needs to be integrated some how with MW3.