I have a lot of experience in the industrial SCADA domain. I largely agree with you, but I will say that historically most installations have had all the relevant source code available to them, or owned by them.
In most cases, the limiting factors for lifespan were:
1) Inability to get replacement hardware
2) Inability to find anyone who can understand the source code.
There's really no way around issue #1. Having the software source doesn't really help that much because most of the time they'll use "migrations" every 10-15 years to rewrite the code using updated understanding of how they want the plant to work. Kicking off a SCADA upgrade is used as a wonderful convenient excuse to drive a lot of meetings/paperwork processes to define "How can we improve safety, improve reliability, make life easier for the human operators, etc?"
Nowadays, the thing time-limiting many SCADA installations are licensing for Windows LTSB and PLC/DCS vendor software. Often times newer versions will require new Dell/HPE servers for compatibility. It's expensive, but also not expensive enough to focus on changing.
The main point is that while licensing artificially limits "longevity" of a machine, closed-source does not. Instead, unavailable replacement hardware limits "longevity" more than "closed source" does.
If/when Windows Terminal integrates sixel support, any cheap laptop should be able to do that OOB (some of them with a USB to serial adapter of course)
From what little insight I could gain, I agree about the hardware problem. The customer I was talking about was nervously trying to find a reliable supplier of motherboards with ISA slots and parallel ports.
I really love the nostalgia this kind of hardware stirs in me, but I am glad I do not have to deal with that kind of trouble. (A few years ago, I read on another forum about an IT guy getting a call on the weekend from a desparate customer looking for an HDD using some standard that predates non-S-ATA... MFM, I think?)
Luckily for that guy, someone has made a MFM-to-SD-card with arbitrary command and geometry transformation recently, it it has turned out to be great. There are MFM-to-SCSI and even SCSI-to-floppy interfaces. The great thing about SCSI in the middle is that it's the same protocol supported by systems today so you could then just convert using generic hardware and software available right now. The system on the other end is none the wiser and thinks everything is still the old interface with the old parameters.
In most cases, the limiting factors for lifespan were: 1) Inability to get replacement hardware 2) Inability to find anyone who can understand the source code.
There's really no way around issue #1. Having the software source doesn't really help that much because most of the time they'll use "migrations" every 10-15 years to rewrite the code using updated understanding of how they want the plant to work. Kicking off a SCADA upgrade is used as a wonderful convenient excuse to drive a lot of meetings/paperwork processes to define "How can we improve safety, improve reliability, make life easier for the human operators, etc?"
Nowadays, the thing time-limiting many SCADA installations are licensing for Windows LTSB and PLC/DCS vendor software. Often times newer versions will require new Dell/HPE servers for compatibility. It's expensive, but also not expensive enough to focus on changing.
The main point is that while licensing artificially limits "longevity" of a machine, closed-source does not. Instead, unavailable replacement hardware limits "longevity" more than "closed source" does.