"Butterfly" isn't synonymous to "unreliable".
Heck, it doesn't even necessarily mean low key travel, which some people seem to dislike.
I've yet to see data to suggests the 2019 iteration is any less reliable than previous "Scissor" keyboards.
Should Apple actually decide to go back to a scissor-type mechanism for whatever reason (PR would be one), that won't magically give you better reliability. And if you expect increased key travel, prepare for disappointment.
I'm willing to believe the 2016 iteration of the "butterfly" keyboard may have had significantly higher failure rates than previous "scissor" keyboards, although mine's been fine.
However I strongly doubt Apple would continue selling millions of Mac notebooks with catastrophic keyboard failure rates. That's quite a lot of free top case replacements..
Post-2016 models being included in the warranty program seems more like a PR move than anything else.
The rumoured 16" apparently may have a new keyboard mechanism. It could be assumed that if the 16" doe appear, and if it has a new keyboard, then we'll get a new 15" with new keyboard at some point too. But there are no firm details, nothing but speculation.