One question that comes to mind is why you'd try to forecast 10 weeks of work for a Kanban team. If the team really works as a Kanban (continuous flow) team then aren't they just pulling the next story in line?
I have a mixture of Scrum, Scrumban and Kanban teams in my subscription and the pure Kanban teams simply don't use timeboxes or Team Planning. If I know a Kanban team's throughput and cycle time metrics then I have everything that I need in order to predict what we can accomplish in the next 10 weeks.
If you feel that you must use Team Planning then your idea of a single 10-week iteration would technically work and let you use the tool but it seems like a lot of overhead for little value. If there are more details about your use case that you'd like to share then please feel free and we can continue the conversation. Hope that helps.