Some old UPSs and industrial machinary use RS232 connections. This can be solved by other means (e.g. USB to RS232 adapters), but virtual com ports are not helpful there.
I use virtual comports (with an FTDI adapter) every day to control industrial instrumentation, and I'm honestly curious to know specifically why they are not helpful in your case, so I can be prepared in case any of my clients experience the same issues.
Does your equipment require the higher voltage levels (I don't remember the last time I saw any that required the full 12V), or do you need all the handshaking lines, or is it a timing or latency issue?
Our assessment was that latency would be a problem for $client. Eventually, it turned out the "just throw ancient hardware at it until it dies" was far more efficient then going along with it.
