Ordering the posts by number of upvotes means that each vote has equal weight

Exchanging upvotes will then become even more popular, as will creating fake accounts to upvote your own content. This isn't an argument against your idea - anything that gives the reader more freedom is better, and readers would become aware of this way to scam the system.

Months ago I proposed filters that would serve like channels. This is similar to tags, but anyone can use any tag, whereas with these 'channels' only the creators of the channel can authorize content. So, you would click on the @Curie channel, let's say, and everything upvoted by curie would come up. You could click on the @steemSTEM channel, the @SteemDeepThink channel, etc. So these channels would be the equivalent of channels like BBC, or MTV, or magazines like Nature, etc. They would each have their expertise, cater to specific interests (or not), and would vie against other channels for quality, and for the reader's attention. This would be a good way to sort the low- from the high-quality posts.