An argument from that side is that the video portion is mostly software related, as the processing power, the sensor tech, the media, etc. are shared. This isn't much different from a smartphone that will take both stills and video.... there must be a considerable subset of people who fit into that group or Canon wouldn't bother with the nice video features. ...
So, then the question becomes, how much will the software cost and will there be additional costs attributable to the video section? The higher end models can absorb these extra costs easier. The lower it goes, there are more and more compromises and, of course, lower demands from the eventual consumer.
PS. Of course, had XT-3 not been firmware destructed or had Sony A-series not been crippled with 8-bit, the "compromises" would have been fairly insignificant.