Has the presumption of innocence now been formally abolished in the USA?
It hasn't.*** Formally, the defendant is not required to prove innocence at any standard. And the state is required to prove guilt beyond a reasonable doubt.
That happens at trial, when it happens, though. So we'll see.
The formally non-abolished standard for arrest is probable cause, btw. Same as searches, etc.
Are neither evidence nor motive any longer required?
Proof of motive has never been an invariable requirement for either arrest or conviction. Because they're inherently not capable of proof or disproof, more often than not.
Evidence is formally required for the state to meet its burden of proof in court. Same for probable cause, though lower standard. It's not unusual for that to be merely a formality in both cases, though. Most of the time, the public neither knows nor cares enough in either for this to matter, but fwiw:.
There's no burden on the state to prove to random members of the public that each and every piece of information and/or representation they come across in the media or online is or isn't anything, no matter where it came from or what it is, at any point in the process. Especially without being asked. All you get automatically is:
Proof of guilt beyond a reasonable doubt in a public courtroom in order to convict.
If non-parties want to know more than that and it's not in the public record, some effort is likely to be necessary. So when the questions non-parties to the matter haven't addressed to the state aren't answered the instant they're expressed, there's usually no formal significance for due process at all, one way or the other.
There also might or might not be answers available at some/any time. But it's impossible to say in the abstract. Someone has to care enough to find out.
Oh! Almost forgot: Probable cause sufficient to withstand challenge has to exist for the arrest to be made. Formally. But that's a part of the suspect's rights. I'm not sure when, if ever, it has to be produced for the public at large. But there's more out there than they usually ever show already.. It's enough to meet the standard. And he hasn't challenged it. So moot point, in formal legal terms.
Because this whole thing -- including this thread -- makes a fantastic, literally unbelievable, spectacle. It's just like a movie. (How could it not be?)
I think it's probably an individual-effort thing there, too.
ON EDIT: Except for when that enemy combatant shit is in play, in which case: Yes, it pretty much has, formally.
Goes without saying.