The NFL could do that but then they would leave themselves wide open for a lawsuit just like MLB did over the "collusion" issue. Clarett is certainly not a first round pick and maybe not even the second round but if he is not drafted at all you can bet your last dollar that his attorneys will file a lawsuit alleging collusion.
I don't think they NBA thing will happen to the NFL and it shouldn't hurt college football like it has basketball because NFL teams drafted based on talent not potential. No one will want to waste a draft pick on some project that may not pan out in 3 years. If anything, you might have a few opt-out this year and next, but things should calm down when those youngsters don't get drafted.