Yeah, I'm guessing that instead of a placating op-ed for liberals, it's more of a calming signal for establishment Republicans.
I think I like your take better than my first one. In either case, the op-ed wasn't targeted at Trump's base voters, who seem to genuinely approve of his most extreme positions and won't read it or believe anything about it anyway.
But you've probably done a better job of identifying the real target audience than I did. An op-ed published by an establishment republican in order to reassure other establishment republicans that they are subverting Trump's stupidity is not too far off from my original assessment that this was "written by a Trump loyalist who is just trying to calm the impeachment cries" but farther away from my thought that "the target audience for a NY Times op-ed is just liberals." It's probably not liberals, it's probably conservatives that don't like Trump.
edit: I'm reading all of today's denials from various suspected authors of the op-ed. They all seem very carefully worded to me, and I suspect it may have been authored by two (or more) individuals together. That would allow everyone involved to semi-legitimately claim they are not responsible for whatever part of it they wish to deny.
edit 2: a more careful reading of the op-ed makes it clear to me that "senior official" could mean lots of things, including any one of the literally thousands of political appointees at obscure government agencies (quick, someone name the director of the Bureau of Land Management without googling). Most of these people have never even met Trump. It's probably not John Kelly or Jeff Sessions who wrote that thing, it's probably some unknown bureaucrat that nobody has ever heard of, who is trying to highlight that their obscure agency is still going about it's business despite Trump's continuedl efforts to undermine everything.