With the Conservatives and Labour roughly equal in the polls, a Labour/SNP alliance is still likely. Let's look at another possible scenario, which none of the parties want to talk about.
The Conservatives could win enough seats to be the largest party in the Commons, but not enough for either a majority (326 seats) or a repeat of their coalition with the Lib Dems. And the combined Labour/SNP bloc could also have fewer than 326 seats. This scenario happens if the Conservative lead over Labour is between three and six per cent, and the chance of its happening is around 12 per cent.
This would happen if, say, the Conservative support is 35 per cent, Labour are on 30.5 per cent, and the other parties are as per the current polls. Then the number of seats won by the parties are: Con 300, Lab 265, SNP 48, Lib 15, DUP 8, Plaid Cymru 3, SDLP 3, Green 1, UKIP 0, and Others 7. The Conservatives are clearly the largest party, but Con+Lib=315, which is not enough for a majority. However Lab+SNP=313, which isn't enough either. The only two-party coalition which would work is the Conservatives and the SNP. But Nicola Sturgeon recently said the SNP would "stop a Tory government getting off the ground", which suggests the SNP would vote against a Conseravtive-backed confidence motion.
But something needs to happen. There are three possible options, none of which is very attractive.
The first option is to cobble together a multi-party grouping that has a small majority. Possible examples are Con+Lib+DUP+Plaid=326, for a majority of just two seats; or Lab+SNP+Lib=328 which has six. Small-majority governments are vulnerable to backbench rebellions, defections and by-election losses in the best of times. In the context of a three or four party coalition, those stresses would be a real challenge.
If there is no majority government, then the opposition parties could vote against the government in a no-confidence motion. However the new Fixed-Term Parliaments Act would then trigger a fresh general election if no government can be formed within two weeks. It's hard to predict how the fresh result would be different. The Conservatives might benefit if people felt that Labour and the SNP had been obstructive, but it would be an uncertain and speculative venture for all parties.
The last option is for a minority government. A party grouping with fewer than 326 seats could win a no-confidence motion helped by some opposition absentions. This avoids the compulsory new election. But the minority government would have to build a fresh coalition for every Commons vote. And without a "confidence and supply" agreement, there is no guarantee that even the budget would be passed. In short, life would be much more difficult for a minority government.
This meltdown scenario is unlikely, but it has a real chance of happening. Perhaps it would be the natural end for a campaign without a clear winner.