This is a great question!
Right now, our plan is to start recommending courses A-F beginning in August of 2017. At which point, Courses 1-4 will become less visible, but they will continue to be around indefinitely, though it might get hidden.
We have a rough translation of these courses:
Courses A & B ~ Course 1
Courses C & D ~ Course 2
Courses E ~ Course 3
Course F ~ Course 4
If you do decide to make the transition, and all of your students have started Course 3 (for example) then you should be able to transfer all of your students over to Course E and have them continue from there. The puzzles aren't 1:1, but they get the same ideas across.
At this time, we are not planning to do any future upgrades to Courses 1-4, unless we are rolling out a new tool that helps every Fundamentals course (like the angle helper and End of Stage extras.)
Hope that helps!