John Sides has an informative post up confirming the intuitions of Ezra Klein and Greg Sargent that new Senators are likely to be a source of internal reform. John counts 27 Senators seated since the 2006 elections. To add to that, since significant internal reforms during this session of Congress appear unlikely, there will be at least thirteen new Senators in January 2011, although three of those will replace other new Senators (in the seats vacated by Barack Obama, Joe Biden, and Mel Martinez). Looking at seats judged "leaning" or "toss up" by Charlie Cook, there are another five incumbents in trouble -- plus John McCain could still lose his primary. So in 2011, about 40 Senators will have served fewer than six years.
My guess is that whether reform is likely, however, depends also on the partisan situation. There are really two ways that reform could take place. By current rules, 67 Senators could simply support and vote for reform. Or, a bare majority of Senators could threaten to impose reform by majority vote, and then negotiate a compromise -- or, if a compromise couldn't be reached, just act unilaterally. I think the former is highly unlikely under current conditions; new Senators may be not respect Senate traditions, but they're extremely likely to be highly partisan.
So that leaves two questions: first, under what conditions would a simple majority favor reform so strongly that they would be willing to accept the costs involved in unilateral action, and if those conditions are met, would the minority try to cut a deal or not? For the former, I think the answer probably involves some part new Senators (within the majority party); some part partisan elevation of Senate reform as a key issue; and some part the prospects of passing things with or without reform (which in turn is a function of whether Senators are looking at unified or divided government, the size of the Senate majority, and other such issues). For the question about minority tactics in the face of majority insistence, and assuming that we're talking about a Republican minority, there's a question about whether conservative activists care more about purity from their representatives than about policy outcomes. I have my guesses about that, but we would have to see.
My best guess? If the Democrats survive 2010 with 55 or more Senators, and then have unified government with at least 55 Senators after 2012, I think the odds of reform, perhaps dramatic reform, are high. If we enter a period of divided government, I think the chances of reform are slim.