I haven't seen this discussed, but I have seen at least one article about it. https://slate.com/news-and-politics/2020/03/trump-cancel-election-day-constitution-state-electors-coronavirus.html. Given Trump's willingness to do literally anything possible to secure re-election and the Republicans party's complete obeisance to him, I see a real possibility that state legislatures controlled by Republicans (see "gerrymandering") could use the pandemic as an excuse to cancel the public vote and choose the presidential electors themselves.
In its entirety, this clause of the Constitution reads: "Each State shall appoint, in such Manner as the Legislature thereof may direct, a Number of Electors, equal to the whole Number of Senators and Representatives to which the State may be entitled in the Congress: but no Senator or Representative, or Person holding an Office of Trust or Profit under the United States, shall be appointed an Elector."
While all the states have adopted popular vote as the means of selection of the electors, that can be changed. In the McPherson case in 1892, the Supreme Court said:
"The constitution does not provide that the appointment of electors shall be by popular vote, nor that the electors shall be voted for upon a general ticket, nor that the majority of those who exercise the elective franchise can alone choose the electors. It recognizes that the people act through their representatives in the legislature, and leaves it to the legislature exclusively to define the method of effecting the object."
That was reiterated in 2000 in Bush v. Gore:
"The individual citizen has no federal constitutional right to vote for electors for the President of the United States unless and until the state legislature chooses a statewide election as the means to implement its power to appoint members of the electoral college. . . This is the source for the statement in McPherson v. Blacker, 146 U.S. 1, 35, 13 S.Ct. 3, 36 L.Ed. 869 (1892), that the state legislature's power to select the manner for appointing electors is plenary; it may, if it so chooses, select the electors itself, which indeed was the manner used by state legislatures in several States for many years after the framing of our Constitution."
While the process would vary from state to state, I assume that through some sort of special session a state legislature could adopt emergency bills to grant itself the right to choose the electors for 2020, depriving its citizens of the right to vote. This would not have to happen on a large scale, just a few crucial states with a Republican governor and legislative majority - Florida, Ohio, Georgia, Arizona, Texas. Am I just paranoid?