Even if some state filings are past their deadline, him getting on in any state (or a write in) is huge.
It would effectively give the black voters someone to vote for other than the weird battered spouse relationship they seem to have with the democrats. If they weren't going to vote for Trump anyways (even though he has/will be picking up more of the black vote than any recent republican), its a direct deduction from Biden.
So instead of purse swinging with the democrats and Biden being locked in his fucking closet, Trump releases something that noone even thought existed; which I'm sure they'll scream collusion and Russia and all sorts of shit about afterwards, but can't do too much because well, don't be racist! Plus its Kanye - hes crazy anyways.
It's basically a planned, flipsided double reverse version of H Ross Perot.