In the UK we have a children's program called Blue Peter which usually has some form of "appeal" going and this is monitored by a "totaliser" which shows progress towards the goal ... The absolutely massive success of these appeals would not have been achieved if the totaliser kept on resetting or moving backwards, never actually achieving or celebrating meeting the target ... and past appeals and their completion are kept for posterity and celebrated - they don't vanish into obscurity even before they have been completed.
Now I am not saying that folders are like children

Seriously - like the idea of the sprints - just feel that the execution/reporting is not conducive to folder engagement ... Yes I know science is the important thing - but if you are going down the publicised sprint route then please, please do it in a way that actually allows sprints to finish !! ... I have no problem with sprints overlapping (watch any athletics meet and many events happen at the same time) but please keep them separate and distinct ... I can even cope with one sprint being paused to let another complete first (like watching the javelin throwers pause as the long distance runners lap past the launch run up).