Why do people care who makes the sensor?
A small-scale snippet from my own life: I worked for Omron's workstation (desk-size Unix computer) department using the Motorola 88000 RISC microprocessor in the early 90s. The key thing about the 88000 was that it wasn't controlled by a competitor. Motorola didn't make workstations. In contrast, IBM controlled the PowerPC, Sun controlled the Sparc, DEC controlled the Alpha, SGI controlled the MIPS, etc. These were all competitors with us.
This mattered because we figured that the latest-greatest CPU in say the PowerPC line would always be available to IBM first, and their workstation team would get better support from their microprocessor team than we would. Finally, the IBM microprocessor department would probably weight the IBM workstation department's needs hopes and wishes a little more strongly than our own.
Motorola decided to partner with IBM and make a single-chip PowerPC that would be pin-compatible with their 88000 line, which they'd then discontinue. (IBM's PowerPC was actually a chip set, not a single chip.) Customers of the 88000 would "simply" recompile their software for PowerPC so they thought it was a good migration path. But we felt a risk, so as long as we had to change CPU's anyway, we changed to Intel x86. Performance was lower but we had probably the best multi-processor Unix kernel, which means our 2- or 4-processor x86 would outperform anyone else's, and the x86s were so cheap we could sell a multiprocessor box cheaper than competition could sell a single-processor box with an expensive, low-production CPU.
So now back to Canon: we're not buying today's camera, or today's lens. We're buying into a system. If Canon were to base all its cameras on Sony (say) sensors, it would be hard to imagine Canon could do as good a job making cameras around those sensors as Sony could. We'd expect the Canon to be a bit more expensive (due to more expensive troubleshooting with a different company's sensor department), and, probably always second to market with a given sensor. Even if got sensors at the same time, it is inconceivable that Canon cameras would actually leapfrog Sony cameras by getting a Sony sensor that Sony cameras couldn't obtain.
The fact that Canon's making its own sensor for THIS camera hints that they'll probably be making a LOT of sensors. (Canon wouldn't just gear up to make one senor.) So, this news hints that potentially, at least, Canon will spend more time getting leading-edge sensors that meet its camera needs well, from a team that supports the camera team efficiently.