Regarding the wealth idea, bit similar: there was
2 year wealth contest some years ago.
Though yeah, maybe wealth challenge should have a subcategory of "no metalsmithing". Otherwise, if given a choice of embark and embark preps I'd be surprised if quicker runs would reach spring migration to bring them above 20 before hitting 1 mil - just single exceptional candy mechanism attached to one masterwork building is already two thirds the way there.
First Legendary X skill dwarf is interesting, however, being the sort of thing that may be more widely useful. Simpler options go for just nonstop quick jobs, i.e. mining soil - with a burrow so that other dwarves will feed/water them and so that they'll not sleep, with spot of prefocusing to increase speed.
However, I'd be more interested in cases where one can't just feed jobs, like in first Legendary Animal Trainer. Embark with doggos, train them, and then trap and slaughter?
Of course, might want to prohibit or disallow migrants, at least as a subcategory, otherwise may be case of "embark with doggos, get Great Trainer in first wave, have trainer train them". Not that save-scumming a migrant wave for Great X isn't a valid option to obtain one, doing it kinda amputates the challenge for training part.
Another more interesting case would be "first Legendary Shield User+Armor User+Dodger" in 43.05, as all training of the first raises latter two, while latter two have exploits to amputate their training time. First Legendary Teacher is similarly interesting due needing multiple skills to work.