All gambling winnings are reportable taxable income, even if they are not reported on a W-2G. If you were to be audited, the IRS can look at every transaction in your bank account and identify all the gambling winnings that you didn't report, and assess taxes and penalties, and the burden of proof is on you (not them) to show they are wrong. Raising the reporting threshold would make it easier for people to avoid taxes, not change what is taxable, so I don't think that's likely to happen.
