It's a Cambrian explosion of complexity. Very innovative space and cool ideas are being tested. I don't know how to check fully either. I just react to what I do know and hope it is good enough for now. We need some sort of better feature detection, or maybe we need to better utilize what we already have. NIP-11 has "payment_required" which is defined as payment for ANY action, so such relays are completely unsuitable for inbox/outbox/dm. "restricted_writes" means it won't be a good inbox. But then there are more. How can you deal with the posting policy? You have to just post and hope. Your PR #1924 and @arthurfranca PR #1969 should be combined. Neither of them help explain however if the relay would be a good inbox or outbox.