I have been thinking about renting it as well just to make sure it isn't for me. I have really studied the handheld footage from the C70 on YouTube and it always seems to have this jittery look no matter what they did; even basic standing still panning and tilting movements seemed to have this slight jitter that just isn't present in cameras with IBIS. Maybe they just have bad hand holding technique but I can't be sure. For me, running back and fourth between photography and video systems at events, there's no way I have time for a gimbal let alone a tripod so handheld performance is key for me to replace the S5.
On a gimbal, tripod, monopod, etc. of course it looks fine, and of course slow motion footage looks fine, but that jittery look really bothers me. Maybe I am just looking too hard for it, but lack of IBIS is really my main show stopper. Maybe if I rent it and try it for myself I'll see that I've been overthinking it.
I did consider the R3 when it was announced, but a lot of the price comes from making the sensor readout so fast and since I don't shoot sports or fast action, I would be paying a premium for a camera that is still lacking WFM, False Color, ND filters, needs a separate XLR adapter, etc. Canon continues to excel at ensuring their market segmentation stays in place and their cripple hammer never rests.