It can be hard to make a business case for something like that, so I'm somewhat sympathetic to their position. I've run into the same problem: the cost of changing can often be greater than the amount you, or the customer, will save by doing so. As far as future proofing goes, my experience is that no one cares until they can't buy parts. Then panic ensues.

At my last job, we kept running into this problem with one customer. Every time they placed an order for the hardware we built for them, it kept getting more and more expensive because we had to search for obsolete parts and charge them a premium. But the amount that our price increased was dwarfed by the amount of money that they made selling their machine, so they literally didn't care. And as long as they happily paid us, we didn't really care that much either.