Teardown shows Apple's latest effort to fix MacBook Pro keyboard
What did Apple mean when it said it changed materials to improve the keyboard on 2019 MacBook Pros? You should now have a better idea. iFixit has torn down the laptop to reveal at least a pair of changes to the butterfly mechanism that might affect reliability. To start, the switch cover now appears to be made from polyamide (aka nylon) instead of polyacetylene -- it's not certain just how this improves the situation, but it's a conspicuous change. There also seem to be changes to the metal dome switch, possibly involving either a new alloy or heat treatment. The added resilience could prevent the switches from breaking or deforming due to wear and tear, heat or other common culprits.
There don't appear to be dramatic changes to the keyboard design, not to mention the rest of the machine. Whether or not that's a problem has yet to be seen, but it does mean that the keyboard is just as costly (at least for Apple) to fix as before. Apple will likely have to replace the top case assembly, including the battery, speakers and Touch Bar, if there's a fault with even one key. This might not be as serious an issue as before if the keyboard is more trustworthy, but it's something to consider if you expect to keep using the system well after its warranty expires.