Regarding NDK, from what i have heard you won't get it unless you have venture capital sitting on your board of directors
I did quick experiment and I am ready to make a SWAG
statement that, no - Roku as platform is unable to handle simultaneous remote key-presses. I did the experiment only with BT and IR remotes though, you may want to try it too: get small piece of code to loop and print the roUniversalControlEvent codes. Press&hold one of the buttons and start pounding other buttons, observe results. In my try with BT remote, after initial key-down event for the "stuck" key, there is no reaction to any other button until the 1st one gets unstuck. The IR remote behavior is slightly different: each new button generates "up" followed by immediate "down" for the stuck key.
Now why do i jump to hasty conclusion: even if you hit Back or Home, nothing happens - which (almost certainly) means that does not make it to the player, otherwise Home would be exiting the channel. Do let me know how WiFi remote behaves, i can't find mine right now.
Most likely this is limitation of the remote hardware design, kind of how keyboards have limit to how many simultaneous key downs they can recognize. If it weren't, that may theoretically be fixable in future update to BT and WF remote firmwares. And maybe s/o Roku* will throw light on this
ps. for grins&giggles, i just tried my iPhone remote app at that and even its touch screen does not play nice: <<_down, >>_down, <<_up, >>_up leads to 8, 9, 109 - instead of expected 8, 9, 108, 109 - with 108 getting lost altogether. I can probably figure out what iOS is doing here re touches but what's the point, since there is no physical remote that can do this.