We also know that the original proposition floated exempted all 501(c)(4)s:
Could the NRA or other groups succeed in watering down the bill enough to alienate the watchdog groups that now support it? Leonard, of the League of Women Voters, pointed to a proposed amendment from Rep. Heath Shuler (D-N.C.) as a possible deal-breaker for his group. The Shuler amendment [PDF] would exempt any 501(c)4 non-profit that finances election ads using only individual donations, as opposed to corporate money, from the billâ€™s disclosure and coordination rules.
That was from a week or so ago, so we know that was at least tried, but the sponsor was concerned that they’d lose the support of the groups pushing for DISCLOSE:
Looking at it, it would be a mistake to eliminate all [501(c)(4)] organizations from the conversation … That’s why we settled on a provision that said, for well-established C4 organizations that have dues-paying members that aren’t trying to hide from anybody — that would be the test.
So the deal would appear to be the result of the sausage grinder, rather than any purposeful conspiracy to freeze other groups out of the process, or crap on the First Amendment, as NRA is being accused of over at Red State.