IF Canon is holding back Mirrorless because they fear it will take away from DSLR sales they are being guided very poorly.
Frankly I do not believe a company like Canon could be so completely naive.
The competition is SONY (et all) If Canon sells Mirrorless, they are making sales. It should not matter to Canon which product they sell, it should only matter if they lose market to competitors.
The pitfall of large publicly traded organizations like Canon is that they very often prioritize optimizing earnings in the short-term vs setting the business up to succeed in the long-run. In the short-term, it does not make sense to invest in the R&D, and tie up manufacturing assets to basically sell a mirrorless body to someone who would have bought a DSLR if it were the only option available. Particularly when the market for cameras is declining overall and Canon has other business units that have more potential upside.
This sort of mentality is what has buried companies like blackberry, blockbuster, Microsoft etc though. Not saying that canon is headed that route, but I can understand the short-term reluctance to release competitive mirrorless cameras even if it will hurt them in the long-run.