Interesting thoughts, I never thought about this and don't have any experience, so I'll leave the taste evaluations to those living on the side of a mountain. I hope Novo Coffee
can post some information from their experience, as they roast and brew in Denver, Colorado at an elevation of 1600m (5,280ft). In Denver, water boils at 202F (95C), pressing up against the espresso brew temp. In Bogata, the issues increase. There, water boils at 196F (91C). Given that water boils at that temp, I think the boiler would be a few degrees even lower than that. And ironically, unless WBC rules are changed, every competitor will receive a 0 on their espresso due to failing to comply with rule 2.2.1.C: 'Espresso shall be brewed at a temperature between 195-205 degrees Fahrenheit.'
Perhaps we'll see a very different take on espresso and a break from the standard definitions. I remember talking to someone at last years MARBC/NERBC competition (Jordan Barber?) who worked for a chef in NYC that turned down the boiler temp to something like 160F, pulled 45 second shots and was still getting good shots. While the machines won't be at 160F in Bogata, there will definitely be a difference in shot temp, time and evaluation that need to be adjusted for.