My prediction is another election this year, like in 1974. The Lib Dems will begin by supporting the Tories, on various ghastly measures, gain a concession on PR and then find a pretext to renege on the deal as soon as there's an opening.
Obviously if they can gain traction the Lib Dems will attempt to use it to introduce PR: arguing that with 23% of the vote they are very under-represented in Parliament. This is because they represent an economic stratum which is not clustered geographically. I think however that people voting under PR will vote in new and unpredictable ways. The long term consequences may be splits in the major parties, but even the short term consequences at the next election are hard to call. It won't be 'take the current vote and run it through the electoral machine I just thought of'.
(ETA - delightful to see a high turnout for a change, though I am startled that people were turned away; that should never happen)
You might like this handy BBC flowchart of what happens next. My header is taken from Monty Python's election night special sketch.