This won't do the price guide any good. Expect to see a massive reduction in the amount of people using it, disadvantaging both validated users and those who refuse to validate, leading to the OSRS community pushing for a similar feature to be added to the official RS website and ultimately phasing this out entirely. Unless of course that was your intention.
You got us, our entire motivation for doing this was so we wouldn't have to deal with users anymore. They're such a hassle!
In all seriousness, we realize that's a risk and that's why we're giving so much warning. We will take a hit in activity, yes, but our hope is the improvement in quality and reliability more than makes up for it. 20% of all offers are already made by validated accounts, and that number is rising quickly. Guests can still view offers, and even if they can't post, as long as there are enough offers by people who can, the system will still work perfectly for everyone. Register and get the benefit of passive offers instead of having to actively look for trades. If the time comes and it's just not going to work out, we can always go back to how it currently is.
Given recent developments too, I'm reluctant to ever validate my account and likely never will.
What developments are you referring to? Validation is totally risk-free, and it only takes a few minutes.