Merge with LD and Conservatives into the Scottish Unionist Party. Or, at least, agree with the other two to run only one Unionist candidate in each constituency.
I was thinking about this, and even with my ignorance I admit this may prove a daft idea, but I was thinking that something like this might be a plausible idea. The SNP strikes me as a party that uses progressive rhetoric but is in practice essentially catch-all nationalist, while making all sorts of populist pledges that appeal to people regardless of their views on independence.
A Scottish-based rival to the SNP (let's call it the "Federalist Party") might then attack the SNP on two fronts- they would espouse a "unionist nationalism" along the lines of the former Unionists (there are all sorts of sectarian issues I am glossing over completely here, I know), mixing that with assertions of being the true representative of the "Scottish liberal (maybe that word is tainted nowadays) tradition". As the name suggests, they'd advocate federal constitutional reform. The other approach would be to accuse the SNP of making empty promises and leading Scotland down the path to fiscal ruin, etc; that while they rail against austerity, their bid for full fiscal autonomy would necessitate far more severe austerity or complete insolvency. This they could do with the credibility of a "Scottish voice" that the SNP's critics have not enjoyed.
It
would be a centrist catch-all party, yes, and while would initially draw the bulk of its base from the Lib Dems and the Tories, yes. They would probably need entirely new faces, but they would need to take (back) 1/3 of the SNP's support- this would the "traditionalists" who might have once voted for the Unionists and former Lib Dem voters. A "non-aggression pact" with Labour in their old safe seats in the central Lowlands
might be a good idea.
Again, I don't know if this is even a good idea, much less its plausibility. But if they were able to simply get a share equal to what the Lib Dems and Tories did in 2010 they'd have 35%. This could be a terrible idea, yes, but I'd like to know why. Also, I'd like to know why the Lib Dems did so well in the northwest Highlands.