I don't know if he will release more, but there is good reason not to.
1) We know the Obama campaign intends to talk about everything except his performance, the percent unemployment, the public's disapproval of his handling of the economy from polls, the public's view that the country is on the wrong track from polls, the unpopularity of his signature achievement, the health care law from polls.
2) The strategy must be a negative one to try and discredit Romney by having enough people view him as an unacceptable alternative so that they are stuck with Obama. I think this strategy is common knowledge.
3) There are two approaches being used to implement this negative strategy:
a) Not just misrepresent, but lie about the underlying facts. Examples of ads that have been discredited by independent sources include GS Technologies, Outsourcing, and Bain tenure. Even after they were discredited, the ads continued to run and the lies were continued by Obama campaign officials and Obama, himself. That demonstrated not faulty research, but a deliberate intent to deceive.
b) Use actual facts but take advantage of most people's naivete regarding finances, especially of a wealthy person. The most obvious example is the insinuation that there is something shady and unpatriotic about an overseas bank account. The notion is absurd. Interesting that many top Democrats also have overseas bank accounts. They are useful when trading in overseas markets. There is also deliberate insinuation that any form of tax avoidance is unethical, deliberately blurring the distinction between tax avoidance, which is legal, and tax evasion, which is not. Most people living paycheck to paycheck without any form of investments are probably unaware that legal tax avoidance, i.e. reducing tax liability is common and good practice in estate planning.
4) The point of giving Obama's team hundreds or thousands of pages of complex returns would only give them fodder to fabricate new diversions from Obama's performance on a weekly basis. "Oh my gosh, he has an account in Monaco, can you believe it....He's soooo out of touch Millie cause I don't have one." or "look at that deduction he took in 2004. I bet he is a felon and could go to prison."