Anti-trust (at least to me) has a connotation with trust-busting and splitting up companies, but I'd be interested in the ramifications of restricting Ticketmaster to creating contracts no longer than, say, 6 months.

On one hand, free markets involve sellers and buyers coming together freely which exclusivity contracts prohibit, but on the other hand exclusivity contracts are nominally voluntary agreements which is a free exchange. Perhaps free-exchange simply isn't a useful framing here.

This could be a headache for venues. The financial arbitrage is too good for them, they have almost zero risk of having their venue empty.

6 months would not make sense, when people routinely buy tickets for concerts 12-18 months out.

Trust busting exists for this very case. Shorter contracts would solve nothing because the market is as far from free as it can be and the one in charge has no interest in changing that.

The busting and splitting up is a hard tool, but anti-trust has many other tools at their disposal, including maintaining status quo (i.e. refusing the merge of two companies). Disclaimer: I don't work in the US, so I'm not sure if anti-trust there is heavily biased there to this heavy duty tool, but I do know they have plenty of other tools

No chance of that, they're based in America