I've suggested this in the past, kind of like playing your joker in It's a Knockout. One or two a month, for writers who meet certain criteria, e.g. over 20 stories published in boosting pubs, could self-nom for access to boosted distribution.
I guess the Medium response would be that it would end up too resource-costly, for little benefit for them.
But this is one of the problems with the Boost, I feel. It's great for nominators, good for readers, OK for writers so long as they are getting a fairly regular stream of pieces boosted (though still anxiety-inducing), but absolutely crap and frustrating for the majority of writers.
Most of the people who provide the platform's content get a fairly shitty deal, and even the occasional benefits can feel like a second bowl of gruel at the orphanage.
I would be trying to change that distribution of benefits if I were in charge. But without access to the numbers, it's impossible to know what would be feasible. And what system (if any such exists) wouldn't end up being abused and gamed, spoiling it for all the nice boys and girls.