The wire that enters the top tube has to run back towards the head tube and then enter the downtube from there.
No space in the seat tube since the seatpost is there for the wires to pass from the top tube into the seat tube.
JC41 never rattled for me
If you use internal battery, you will have to use the SM-EW90-A/SM-EW90-B junction for the shifters. The SM-EW67A-E will only work with the BTR1 battery mounts.
Had me thinking. Because I have an ISP, my wireing could theorectically go either way. So I just checked, and yes my wireing goes into top tube, and then forwards to head tube, and then down the downtube.
My junction box is resting on top of my Bottom Bracket Shell.
I'm not sure if the new internal seatpost battery will fit, because of the Aero ISP? I'm guessing not.