[...]I don't see a Republican-lite winning against the genuine article.
Interesting. Why?
In a strictly two-party system, a Republican-lite that gets past the primaries has a (theoretical) advantage over a "true" Democrat, in that it captures those votes which are to the right of a true Democrat but to the left of a Republican-lite.
Republicans are big on hating Democrats; the fact that Clinton is married to former president Clinton and played an influential role in his policymaking is not lost on them. If she plays Republican-lite as the Democratic presidential candidate, any potentially sympathetic voting bloc would dismiss her as a two-faced phony that belongs to the evil socialist librulls.
Meanwhile, progressives would have to ignore her voting record and corporatist ties to vote for her. Obama ran a good, if ultitmately duplicitous campaign in 2008 and got the progressive vote. If Clinton decides not to take that approach and instead plays the hawkish more-Republican-than-them card (which she did when running against Obama in 2008), the progressive base would be alienated and we may get a similar progressive turnout in 2016 as we normally get in the midterms. This would be devastating for any Democratic candidate and would basically hand the election to Republicans.
So the obvious risk of an R-lite is the left vote splitting with a third party, which requires a viable third-party leftist candidate. Is there one, or a strong expectation that one will show up in the next two years?
Personally, I am willing to endure handing Republicans a high-profile election if it means a significant chunk of voters abandon the Democrats for a third party. This is the sort of tactic that pushes the Democratic party platform to the left and it's something progressives desperately need in order to gain any sort of traction in policymaking.
As for viability, third parties won't be getting much money from the capitalist elite and they won't be getting much if any attention in the mainstream media. This always hurts the chances of an otherwise great candidate from the start and it's a big reason why we need to get money out of politics and why we need a more independent press.