Reminder: the Boy Scout Motto is "always be prepared." Other posters have said it. Never put all your eggs in one basket. Going on, it pays to have credit cards that access the Mastercard and Visa network. You never know when a network failure could take place!
Starting Score: 807 Current Score: 828 Goal Score: 850
If I were to close all my accounts except my Citicards, would that have any bearing on being any easier to obtain more credit with Citibank
As others have pointed out, that's not the only concern you should be thinking of. You may not see the need for credit form others now but things can and do change. Consider the full impact of closing those accounts (impact on utilization, impact on AAoA down the road, impact on number of accounts, etc) as well as the risk of relying on a single creditor.