I think that brownout lowvoltage tests are only part of the problem.
It is not only how low voltage can go the receiver, but it also it's ability to handle power loss, how long can the receiver stay locked when input voltage is 0V (time in ms.) The main importance is the receiver should have a proper buffer capacitor over the RX chipset. Digital servos and speedcontrols are switching devices, they generate current peaks and ac on the power lines especially the cheaper ones can give dirt on the lines. Also locked servo's can also give very short spikes.
How does power circuit for the chipset in the receiver work:
Mostly receiver chipset are protected for reverse polarisation > diode in serie (or possible resistor in serie, diode to ground) > than there is a low drop regulator or a resistor and zener diode, feeding the chipset with stable 3V3 or lower. (When going below 3v3 normally it still works, depending on chipset in some case down to 2v))
Then there is a capacitor. This is were most receivers lack, most receivers use very small capacity buffer capacitor. Most of time SMT Tantal capcitor 10Uf or so. Quality capacitors are expensive and big in size. A small capacitor can indeed filter away some high frequency noises, but it does not act as a proper buffer.
I recommend all manufacturars to integrate a goldcap or so called supercap, memory capacitor, they act as a small battery inside the receiver and are able to power the receiver even down to 0V, for short period of time. From my experience a 0.1F Goldcap give more than 1 second on my flydream after removal of power
There are many types, fo example this is one;http://search.digikey.com/scripts/DkSea ... =P10791-ND
For instance Flydream and some other manufacturar, provide a big capacitor to plug into one of the servo channels, this is not a good solution. It will indeed remove the ripples from a bad bec, esc or servo. But high currents burst coming from agrassive servo movement (servo overload), will be also powered from the capacitor. So capacitor in parallel with battery power and servo's will not secure power for the chipset. The goldcap capacitors are also many times smaller, but have muc and much higher capacity.
Another point that I don't like most RX have a small range on input voltage, as RX chipset consume very little of power, it is not that difficult to make them accepting wide range of input voltage F.I. 16V - 3V, often they are limeted to 6V.
Maybe RC modelreviews can give it as a recommandation and push market forward..........