*Off the top of my head, there are issues of knowing who the witnesses against you are; USADA's access to evidence assembled for criminal investigations, specifically the grand jury issue; incentives offered to witnesses; the justification for exempting from the limitations period; the appropriate burden of proof; and probably others as well. I stress I am not taking a view on any of those issues, just saying it is legitimate to debate those issues without being taken as rejecting USADA's jurisdiction or asserting LA's innocence.
The grand jury thing is probably a non-issue. There are all kinds of ways round this in cases where someone merely is asked to leave the room. Or parallel interviews and so on.
The limitations period was covered earlier in this thread. To be brief you can argue fraudulent concealment (again see earlier).