Civic has single assembly line for local production. They cant run two models on the single line. Infact most of assmbly line around the world are single. The production is speed up by other means which includes high level of automation.
Also what will be end benefit to have an older and new generation let's assume if they do so? , there will be less and almost zero demand for older generation when new is launched.
I personally don't think we will have X and XI rolling out side by side