I'd like to see some of the moderately priced speakers of 10-20 years ago that were aiming for neutrality. Things like the PSB Image series, Energy Connoisseur and RC series, Paradigm Monitor series and such. A lot of them can be found on the used market for under $200.
A lot of them have been measured by others in the past, but it would be interesting to see them get the full measurement suite here, see how well the match and see what
amirm thinks of them compared to newer speakers. Or maybe measure the models that haven't been reviewed as much (Energy C-1, PSB Image B15, etc) and see if they are as good as the models that were sent out to the magazines back in the day.