The fact that Hunter has apparently already paid whatever his outstanding tax liabilities were will substantially reduce the pressure on the DOJ to prosecute him for criminal tax fraud.
As an institutional matter, the DOJ prefers not to prosecute people when their defense can stand up and say, "yes, serious mistakes were made, unfortunately, but the tax code is so complex that it's understandable, and at any rate, once the IRS brought these problems to Mr. Biden's attention, he cooperated with them, agreed to the amount of unpaid taxes, and paid those taxes, plus considerable penalties."
Most juries will sympathize with the first point, particularly small business owners, and they will be very amenable to the argument that payment in full washes away all tax sins.
So, unless there are clear grounds - based on the DOJ tax division's own institutional perspectives - to go after Hunter for tax fraud/evasion - i.e., some clear reason for why he should be punished beyond the monetary penalties (which can be very stiff all by themselves) - he's unlikely to be prosecuted.
