Developers are always busy. We have lists of bugs and feature requests from many places. We don't usually work through them in chronological order: they are prioritized in different ways, based on the urgency of an issue, the effort required to fix an issue, etc.
That said, developers like quick wins and low hanging fruit. If people do some testing and prove which permutations of kernel settings, firmware and hardware are troublesome and which permutations are good and also provide log data, the developer behind the code might recognize what the problem is and make a quick fix for it.
If the developer has to obtain hardware and do the tests himself, he might lose a day on it, in fact, he might never get around to it.
To give a personal example, I often spend a few weeks working on a feature or major change to some code and then before making the official release, I look over the bug list for anything that is easy and I fix those things and include them in the release. If a bug report doesn't have enough detail, I have to defer it to the next release cycle because I can't delay a release for something that I can't reproduce.
I personally have no plan to buy the RX 5700 right now, I was going to skip that generation and go directly onto Big Navi. If somebody else wants to test with one of my kernels using 4k page size, I'm happy to provide some guidance.
If anybody has contacts at AMD to get sample hardware for developers under NDA, there are a few people, myself included, who are happy to test it and provide feedback and sometimes fixes.
