I tend to view Weber in your second-man-in scenario, but I'm sure the club's plans for openers will ultimately fluctuate based on match-ups. The "traditional" opener or trend (in a concept two whole years old), I think, is to preferably start someone with an unhittable fastball and let him air it out against a lineup's top of the order, then bring in a "bulk" guy to hopefully flummox the bottom a couple times through (but only once against the top -- those are the guys you want to keep showing different looks to). Ideally, this keeps your team in the game and gets you to the back end of the bullpen...
With expanded staffs and three-batter minimums, I can envision two sets of openers/bulks that take turns in rotations just like starters. For example -- and these are examples, not my suggestions -- Taylor opens, followed by Weber on Day 4, then Darwinzon opens, followed by Johnson on Day 5. If pairs are effective, they get regular rest and do it again in five days. Best case, this strategy works maybe half the time, and we'll be treated to a cavalcade of call-ups...
... until someone shows he can be stretched out into a real starter who give us actual quality starts!