So, is it entirely possible that we'll just never know anything?
Nah. Short version:
There will be info, just maybe not a televised trial. That will be up to whatever Judge. Should be a change of venue, or at least jurors shipped in from another area. A trial would not happen for at least a year, just some Motions hearings.
They may offer Holmes a plea if he talks. (Assuming he has not already, or in a few weeks when tired of being alone.) If that happens, we will get some written info. However, I doubt an offer would happen. Too many gone. I'm not even sure the family members that are survivors would agree. Something this big will most likely go to trial. There should be more than plenty enough evidence for conviction. So scratch plea, move next to "bench trial."
Bench trial would just be Holmes accepting responsibility (ie. admitting he did it) and allowing the Judge to decide his sentence. No jury involved, which would be helpful to any unfortunate souls that would be called for jury duty.
Then there is an Alford Plea, but I don't think that is even necessary to discuss, but he would still get sentenced by the Judge and no jury.