Comcast in my area doesn't even make claims of upload speed anymore, but my recollection of when they used to is that it was about 10% of the download speed. If you want more than 2 Mbps upload, that 20 Mbps plan wouldn't cut it.
There is a full duplex version of DOCSIS, but its adoption faces some challenges due to how operators have to re-architect their physical networks to support it.
There is also currently a push to extend the downstream spectrum up to higher frequencies, enabling both more downstream bandwidth and also the ability to move the upstream split higher, therefore increasing upstream bandwidth.
(Disclaimer: I work with a client who develops products in this space.)
Of course the actual pricing, availability, etc are also important but I don't think there needs to be a one-size-fits-all model for Internet bandwidth.
Even if the physical plant supported symmetric bandwidth, I would expect different pricing plans for different utilization patterns.
I think I'm around 50 Mbps and it could be used much more heavily, but it doesn't make any sense on YouTube's end to send me a 50 megabit video stream. It's a the storage and upload costs on the provider side limiting that.
Even if you pay extra for Netflix's 4K support, that only needs 25 megabits. It's compressed to hell compared to a 4K bluray, but if we all had faster internet I don't know if that would change. It's lot harder to market the actual visual quality of a video compared to talking about how many pixels it has.
Maybe we'll see whole new services that need the bandwidth, but most stuff that sends a lot of data could be downloaded in advance if you don't mind waiting 5 minutes instead of having it instantly accessible. How many billion dollars are we willing to spend to build out faster networks to avoid that? What's the selling point for very fast streams, we go back to cloud mainframes and all of our devices are dumb terminals that stream our games and the whole OS from an AWS datacenter?