There is an inherent incoherence in a book aiming for both partisan dominance and policy effectiveness, and though it's hard to disagree with any of their policy ideas (thinly laid out as they may be), it can be hard to imagine the Republican Party moving in this direction. Certainly Bush did much to advance this model of an activist government with faith upgrades, but his failures suggest problems and concerns with this approach.
First, you have the money problem. Ross and Reihan are right to suggest that independence comes in many forms and their proposals would decrease overall regulation while perhaps increasing nominal government spending. But as long as raising taxes is apostasy for a certain portion of the Republican base and curbing defense spending unthinkable for another, it's just not going to be possible to balance the budget, no matter how many earmarks you cut (curbing entitlements is a non-starter for both parties). And even if consumption, carbon, and congestion taxes balance new spending, there is still the current deficit and exploding entitlements.
Second, you have the tensions between the "destroy the government" and "reform the government" wings of the Republican Party. It's easy to forget that Bush sold himself as a reformer with results who would work as a bipartisan fixer--a uniter, not a divider. Many of the failures to follow can be blamed on partisans in the first set; figures such as Rice, Gates, and Paulson are responsible for Bush successes in the last few years. So getting GNP right is an issue at least partially of competence.
Healthcare is obviously a big issue, and I suspect Bush's failure to deliver on this will be remembered as among his worst. There actually turn out to be a number of conservative options on this issue, as Ross and Reihan point out. Republicans Romney and Schwarzenegger have tried to insure the uninsured, while even Obama's economic advisor praised the outlines of a plan to end the tax-preference for employer provided health care--that is, McCain's plan. But it doesn't look like it's feasible for Republicans to present more comprehensive reform; even Romney played down his record in the primaries.
In fact, Romney's downfall marks another failure of a modern conservatism to emerge from the myth of Reagan. He first caught my attention as a data-oriented, pragmatic, power-point governor and potential nominee. Then his pro-choice, Mormon, blue-state presence proved to be sufficiently offputting that he was forced on a righward lurch that both failed to properly endear him to the base and marked him as a flip-flopper to everyone else. I would argue that Romney's predicament was less that he's a "slimeball" than it was structural; it's tough to be a competent executive, survive the base's gridlock vetoes, and appear genuine.
In the end, as other reviewers have pointed out, many of these ideas are more likely to appropriated by Democrats rather than Republicans. Ross and Reihan have a curiously outdated view of current liberal thinking. In fact, as Clinton demonstrated, it's possibly easier to pursue socially liberal goals through market means than combine a fetish for low taxes with a heartfelt concern for the working classs. Their agenda isn't unthinkable either--Cameron's Tories are set to accomplish something similar. But in America, such a change will likely require a transforming persona with both right-wing credentials and a capacity for competent governance. Bobby Jindal, who I don't just like because he's Indian, is one such figure--combining support from Gingrich with an ever mounting list of achievements, including on healthcare and education. Sarah Palin may also prove to be another. John McCain is almost certainly not.