not at all.
Canon can take one of 3 approaches:
1. repeat Sony's mistake and use EF-M also for FF-sensored MILCs. it would be technically "viable", but not desirable, since IQ and lens design would be severely limited and compromised ... see Sony FE lenses
2. repeat Pentax mistake with ill-fated K01 and use long flange distance EF mount for mirrorless MILCs. no size advantage for camera bodies and lenses in most frequently used focal lengths range possible.
3. launch new FF mirrorless lineup with a big bang and a newly designed, no-compromises, optimal design lens mount for FF image circle, maximum IQ and size advantages for most frequently used focal lengths. bigger, faster lenses also possible without any technical issues.
most important for canon' decision: compared to scenarios 1 and 2, many more new lenses will be sold in scenario 3 over the next umpteen years! not only new MILC camera purchasers and "crop-to-ff-upgraders" will buy new mount FF lenses, but also majority of existing EF user base will transition from EF glass to new native mirrorless mount glass as they move from dslrs to milcs.
other than in 1987 fd to ef transition there it will be painless for existing customers, since ef lenses will remain fully functional with a cheap little adapter. everybody can decide for themselves if/when they want to upgrade their lenses. new/improved lenses with better iq and functionality (af, is, ...) will however only be available in new mount ... $$$$$$$