In CQ's report on Hastert's decision to retire from Congress, it offers this paragraph on the way, partly under Hastert, caucus leaders in the House were able to concentrate power:

Under Hastert, a Republican-written term limit on the Speakership was abandoned even as six-year limits on chairmen were kept in place. The move solidified the caucus-elected leaders as permanent power centers. Meanwhile, the seniority system eroded. When chairmen cycled out they were not necessarily replaced by the next-most-senior member on the committee. Instead, they were forced to compete with each other by proving their loyalty to the party through their campaign fundraising efforts and voting records.

The chairmen and subcommittee chairmen owed their allegiance to the leadership, which in turn was elected by the caucus at large. The system, which Democrats have largely followed, gave tremendous authority to party leaders to develop and deliver a legislative agenda.

One wonders what this shift away from the seniority system might mean. Could it lead to a more dynamic House, in which new players continually jockey with old players for this newly centralized power? This shift might--in addition to giving party leaders more power--also make the position of party leader a little more unstable; with fewer limits on the power of party leaders, others might find this position more desirable and easier to achieve in the absence of a seniority system. And various congressmen and congresswomen might be more inclined to engage in party leader conflicts (since their positions would even more depend on these conflicts). Of course, with these new controls, the right party leader under the right circumstance could exercise even more rigid control over the House than under the earlier, seniority-balanced system. And you could have both: rigid control with some level of uncertainty bubbling beneath the system. Or so it seems to me at the moment...