But both systems use XBL so if you use the xbox one upload won't 360 users be able to see it?
If you record gameplay on xbox one will someone with and xbox 360 be able to view it?
If the clips go on youtube, then sure.
Yes but its not as simple as saying they use some software with the same name. The 360 does not support DVR and does not have any of the software that enables the X1 to film/view that footage. Different software means incompatibility in certain aspects.
Some aspects like text messages are able to be shared between the two platforms, while others like voice chat, are not. With that being said, the end result is that we do not have any info from MS regarding this issue, but I think the safe bet is no.