Every loophole that exists was originally a political favor to some important constituency. There are always important constituencies seeking political favors, or embattled politicians or parties seeking new allies; so there will always be pressure to create new loopholes.
If a loophole's in danger of going away, its constituency will scream bloody murder. Republicans who vote to eliminate it will be painted as "raising taxes;" ever since Bush I promised not to raise taxes, raised taxes anyway, and then lost the White House, a lot of Republicans have been very afraid of this political attack. So there will always be pressure to avoid closing existing loopholes.
So loopholes are monotonic -- they can only increase over time.
The only way we could conceivably get out of this situation is if our tax code becomes so complex, everyone -- even the beneficiaries of the loopholes -- is angry and upset at the complexity and costs of paying, and decides to support throwing the whole thing out and starting fresh. This scenario probably requires a united government (same party controlling Presidency and both houses) which is willing to make the issue a priority. It's probably not going to happen in this year's election, unless a major event occurs between now and Election Day.