As someone who has never been higher than silver, what does it take - on average - to get to GGL?

As a very rough estimate, I simply took the old TP level of 5000 and divided it by 180, as that's what a long-haul plus a connecting flight would earn in business. It would mean travelling long haul return every 3 weeks or so.

That sounds quite gruelling if done for a number of years. (I guess if you flew first instead of business then that would reduce the flying need considerably.)