While the usual question about this verse concerns who or what restrains, my concern is with what is restrained. I understand why those sold on the Nero theory like this translation because a "him" that "is" being "restrained" makes the man of lawlessness a contemporary of Pauls, but does the Greek bear this out?
A couple of posts in here seem to pick up on the problem. I like one by Dottard and [another] (Has Paul's concept in 2 Thessalonians 2:7 been misunderstood?)
The issue is that the Greek word κατεχω for "restraining" or "holding back" doesn't have an object. There is no "him" being held back. So what is being held back?
Would more justice be done to the passage if we maintain that rather than a person of Paul's time being restrained, what's restrained is the evil that will give rise to such a person?
Can we hold that sin and evil will, when unrestrained in the future, result in a collusion between mankind and Satan? Couldn't we hold that this collusion will be facilitated by the man of lawlessness who is yet to come?