But yea, it will probably never be added due to various security/networking concerns about the results of it. I agree, its a cool idea to add in theory, but there are too many concerns about it and in financial software, thats just unacceptable.
Can you explain which concerns, and why they cannot be addressed? Why would using another port than 8333 be less secure?
I'd say using a fixed port has security/networking problems of its own.
The only potential issue I could find in this topic is this one:
Satoshi pointed out that allowing bitcoin/bitcoind to run on a non-standard port could be dangerous, because if misconfigured two bitcoins might both open and write to the same database.
This could be addressed by storing the port number in a configuration file in the same directory as the database (or even *in* the database). One database will only open on one port, effectively protecting it.
Or use some other scheme to make sure only one bitcoin is running on a database at the same time, such as a lock file. This would be even better, as it doesn't depend on TCP rejecting the second bind to the same port