If the shill accounts you mean newly generated accounts, those cannot vote by default. Another user would have to upvote enough of their content to the point where they can vote. And at only one vote per piece of content. That's a lot of surface area to cover without getting any downvotes to really pull it off. Again, the only real downside that someone else has mentioned is if someone were to buy already upvoted accounts. They would still need to generate more good content (thus increasing their surface area for downvotes) before those account can get more upvote and more "weight." I have not figured out the issue with bought account but unless they contribute content, they, at the very least, cannot raise the "weight" they carry without risking spam content and downvote momentum.
Assume I was to buy 10 accounts with low upvoting power , maybe just a couple.
I could then make a single post that seems kinda constructive on one of the accounts and upvote it on all of the other accounts. While this would be a little suspicious , it would not be enough to be flagged in any way.
That account would gain a lot of upvoting power.
The only way that will not happen is if people give upvotes only for good reasons, just like trust.
It seems like a lose-lose scenario from there , because if it is used as rarely as trust , it will not help much on the forums and if it is used any more commonly , it may create dangers.