Even the OEM firmware doesn't like 256 MB RAM on these SOCs, yes it's jumping through hoops (by hugely invasive cuts into the kernel) to somehow make it just work (performance be damned, features - what features), but at huge costs (in terms of performance, features). Only the bottom of the barrel devices get that little RAM, which is really missed in those devices (the SOC, NSS and wireless cores really need it). There are ipq50xx/ ipq60xx/ ipq807x devices with 'sufficient' (512 MB, but that's already on the tight end) amounts of RAM, as well as enough RAM (1 GB).
These rather huge RAM requirements are specific to Qualcomm's SOCs && wireless chipsets and design inherent, it's essential to their approach of making these work.