good news: after being very patient and persistent, my contact at ingenic put me in touch with a support engineer who confirmed that the limitation on the jz4775's reported maximum resolution (1280x720) is for the *video decoder* not the actual LCD output capabilities. the actual LCD output may go as high as something like 1700x1700 (not at 60fps obviously) but that things like 1280x800 @ 60hz (the crucial limit of the eoma68 spec) are fine, as is even 1366x768@60hz.
however he did kindly point out that if 720p video decoding [for which the full source is apparently available, which is also great] is attempted to be displayed on a 1366x768 LCD (or greater), there is a bandwidth memory limitation between the video decoder and the lcd buffer which would prooobably end up stalling slightly so that 30fps would be hard to achieve, at full-screen.
honestly, i really don't see this as being a huge show-stopper enough to warrant exclusion of a low-cost SoC that could be the first FSF-Endorseable candidate to run GNU/Linux OSes with a decent amount of RAM (2Gbytes).
as i've had the first revision PCB done nearly 4 months ago, that just leaves financing of the first revision jz4775 CPU Card to arrange. i have one potential sponsor: if anyone else would like to help out that would be great. we're likely looking at around $USD 1,500 for 5 PCBs.
l.