In either of your first two scenarios, where does the big-business, Wall Street, Bush, Koch wing fit in?
In any case, I think if the GOP wants to win any presidential elections in the future, they need to ditch the 'Christian right' AND the nativists. It's all about demographics. The African-American demographic is already a powerful voting block, the Latino/a population is only going to keep growing, the gay population is more emboldened and open than ever before and the younger generations are far less likely to be swayed by religiously-informed homophobic positions on those issues, and the percentage of people nationally identifying as atheist, agnostic, or unaffiliated is rising, and now combine to make up a quarter of the population, and that could continue to rise and in turn decrease the acceptance of conservative social positions and increase the vitriol of the nativists/trumpists who still support said positions. Oh, and women generally support the party that wants to give them their reproductive rights and equal pay and more(no GOP candidate has won a majority of women since Bush 41 in 1988).
You simply cannot alienate that many demographics and expect to win national elections.
I agree with you that the "demographic" pool for the GOP is getting smaller. But if they hadn't taken their nativist turn, there is a scenario in which a Marco Rubio-type of candidate can appeal to a broader base, including socially conservative latinos. But now, I truly think that boat has sailed with the Trump nativist crowd (which has some overlaps, but not fully, with the socially conservative crowd and the defense hawks). The pieces simply don't fit together in the same coalition anymore, as Paul Ryan is finding day and again.
This is why I referred to the European Christian right as a model. They are significantly more centrist than Republicans, particularly on social issues (as well as on military spending, to be fair). A non-nativist, less socially-conservative, small state, low regulations and low taxes party, I think, would appeal to a larger segment of the population than the current GOP. It would still try to appeal to the nativist right at times - like Sarkozy in France - but it would be a distinct and viable entity. And it would possibly appeal to centrist democrats in places like the rust belt.