Active ftp is dead. I wouldn't be surprised if browsers don't support it out at least don't default to it since as you said it would break things for 99% of users. Running a server that's not configured properly for passive transfers is effectively a server that's useless. So if it would make someone sleep better at night I'd be fine with removing active transfer support from browser clients. Switch to filezilla if you're a power user or want to do some 1337 FXP tricks.

In ftp, the ftp server is designed to act as the load balancer. (Just have the firewall point each port to a different IP.)

Also, this enables linear scale out, since not all ftp data nodes (not sure what the correct term was) need to store all of the data that’s being served, and you can store multiple copies of each file.

Come to think of it, I’m not sure why HDFS exists, given that you can just use a ftp server cluster for the same effect.

Oh, absolutely! I said it was ugly/stupid from personal experience:) But it's a form of stupid that can be condensed into a single state diagram that would fit on half a sheet of paper, so I'm not super concerned about it.

What? Like OpenSSL:

https://en.wikipedia.org/wiki/Heartbleed

(I mean, I'm not overjoyed at the deprecation of FTP support because I used it just yesterday, but let's at least be honest here. The protocol might be decades old but the implementations aren't necessarily, and if they're being actively maintained there's always the possibility of introducing new bugs.)

The protocol is buggy AF. All that crap about sending data over a separate TCP connection, the weird way you have to deal with state and authentication; ftp is an utter shitshow. Just because a protocol is old doesn't mean it's matured to perfection. Telnet is old, so is RCS, and UUCP.

Many protocols evolve not by being replaced by incrementally better point releases, but rather by being supplanted entirely by a better designed alternative.

FTP effectively evolved into HTTP for this use case, and scp/sftp for the authenticated file transfer use case.

Can you give an example of a piece of software of reasonable complexity (network/file handling, etc) that has solidified like this?

Are you referring to this bit:

and there are other bugs in the implementation which further demotivates the FTP support.

To me that reads as there are bugs in Chrome's implementation of FTP.

Did you take that to mean the author intended to convey the message that the FTP protocol has bugs?