The upshot is that for a regional party to get elected, they have to build a seven to eight figure campaign war chest per seat, because the second it looks like they have a good chance of winning, the national parties will pull a Brinks truck full of nationally-sourced money into their own candidate's campaign headquarters.
And while it's certainly true that money alone doesn't guarantee results (see: Linda McMahon, etc.), if you're running a campaign on $500,000 and your opponent is spending $50,000,000, you're in serious trouble. And it's difficult for a regional party that can't even guarantee the ability to filibuster to raise that kind of cash.
What I think we're more likely to see is what we've been seeing: Not separate parties, but independents with their own personal wealth who are willing to spend it to get themselves elected, and who have enough to make it a fair fight when their money is undiluted by multiple races. The problem is that then the candidates are self-selected and there is no guarantee that they'll agree with each other much less any of the electorate.
(I also think you're overestimating the economies of scale in party fundraising: look how much now happens outside the parties themselves -- independent expenditures -- and directly by specific candidates. It's only at the margins in winnable races that national party funds come in, and even that now has to be weighed against the negatives the national brand can bring. The new pools of money -- from both mass crowdsourcing and wealthy crusaders -- care more about winning than 20th-century party labels... and in the national legislatures independents/other-parties can and will caucus with other groups for the purpose of parliamentary procedures.)