There are several questions to ask:
1. Are the rumors true? It's certainly possible that (for example) Christie's pollster might have tossed in a couple questions about a presidential run, or even something tangential to that, for a focus group even if there's no real serious plan to get it. As Jonathan Chait said this morning, interpreting potential candidates' denials of interest is a fine art indeed, and it leaves all sorts of misinterpretation very possible -- especially for anyone who has an interest in or a preference for a new candidacy.
2. If Christie or Ryan got in, would they be plausible nominees? I'll give the same answer to this that I've always had: they would not. Members of the House don't get nominated, and rarely compete seriously for the nomination. Ryan would be a whole lot closer to Dick Gephardt than to Michele Bachmann, so all things being equal he'd be a more plausible nominee, but that's not saying much. Christie? Again, giving a nomination to a recently-elected governor wouldn't quite be unprecedented (Woodrow Wilson), but there are good reasons it doesn't happen often at all. And all things aren't equal; it's very, very late to jump in from scratch, which is (as far as we know) what they would be doing.
Note: They could get in anyway! I'm sure there are plenty of people close to both who absolutely believe that Ryan/Christie are heavyweights among the lightweights, and sure nominees if they were to get in...and plenty of consultants who would be happy to pretend to believe it if it helps them pick up a nice check (or: plenty of consultants who sincerely believe that they could steer anyone willing to take their advice straight into the White House).
3. If it's not about Christie or Ryan actually getting in, what's driving it? This is a really big question. It could be a few individuals who for whatever reason don't like Rick Perry. Or, it could be important groups within the party who are genuinely searching for an alternative. That's probably very difficult to report on, but such reporting could help us sort this out.
I'll stick to what I've been saying. My guess is that neither Christie or Ryan will actually get in. If they do, I'll continue to call them implausible nominees until proven otherwise. It's not inconceivable that an implausible nominee could win, but I've set the chances at well under 10%, and see no reason to change that now. There's just an enormous amount of grass-is-greener thinking going on here, sparked among other things by the length and, well, invisibility of most of the invisible primary.
And at any rate, I needed an excuse to quote Alex Pareene's reaction:
I dunno, does Chris Christie screaming insults at a room full of random people really count as a "focus group"?