Actually following up on this, it might be possible for free? If the cutoff for gold league is about 500 right now on Beta (as it's usually lower on live servers), and you can get to at least 560 tasks with the free gemstones (+ incidents), if you just speedran the towns you could maybe do it.
MIGHT. depends on the world --> older worlds more likely because in newer worlds player tend to spend more money (more points needed for higher leagues)
but in previous events there wasn't such a BIG HUGE AWESOME buildung in gold league
it gives 1 full event building in 25 !!!! days = 14 per year
compare to the Anniversary event: I got there in gold for free in my live world (old world, the points there wouldn't be enough for gold in newer wolds)
I got a lousy level 1 Key Master's Workshop. that produces NO fragments
I think: many will try
If the cutoff for gold league is about 500 right now on Beta
that was without the announcement what the building can
how high would it be when players already had known that at the event start ??
and we have still 5 days --> 5 cities possible (with time skip even more) = +150 task possible