For me it's clear now that Artix US is not the replacement for Artix, for some applications US suits much better, but for others Artix is fine.
Well it could be a good replacement for higher end Artix devices, as long as you don't require massive IO count some of those old Artix'es have.
But what is interesting is that they effectively undercut their low-to-midrange Kintex-7 devices (again, provided that you won't require an extra IO of Kintex'es). If you look at AU25P vs K325T, in appears that the former is better in just about any metric, and, importantly, it's available with a free license (you have to buy a license to use K325T devices). Similarly, AU10P seems superior to K70T, as is AU20P to K160T - new devices are faster, cheaper, support modern and faster memory and IO standards, and more power-efficient.
Also 16G transceivers allow connecting modern fast ADC/DACs via JESD204 interface, something that was simply not possible before, as these devices typically run interface at 12-16Gbps.