Donald Trump will never, ever, release his tax returns.
There is nothing in it for him. And, "for him" is all that matters. [Remember, Congressman Sanford (R-SC), when you suggest that Trump do something to maintain the integrity of our democratic process that Trump could not give a damn about us, about you, about democracy, about anyone or anything, except himself].
If he releases the returns, he will lose the presidency. If he does not, he may be pilloried for his cowardice, as he should be, but he would still stand some chance. We can reasonably surmise, for example, that he received amnesty from the IRS for squirreling away money in Switzerland, but we cannot show it in black and white.
More important than the presidency to Donald Trump, moreover, is his so-called business. I say 'so-called' because, in learning about what he has done, it seems as if it amounts to inheriting a fortune, servicing the rich, scamming the vulnerable, stiffing his contractors and snookering his investors. As Penn Gillette said, "Trump was unable to sell steak to an obese nation".
Trump's business, such as it is, seems to be dependent entirely on the brand Trump believes he has created. He "sells" rights to use the name to developers, for example, who apparently believe that affixing a Trump name sign to a building enhances its value.
And that, in turn, depends on the perception of high quality and/or snob appeal to that brand.
Once he reveals his taxes, it is likely that that perception will vanish.
It is appropriate and important to keep the pressure on Trump to release his tax returns. He should not be able to escape his responsibility, and he should be continually called a coward for hiding them. Because he is a coward, and not just with respect to his returns.
But, releasing his tax returns? It ain't gonna happen.