Yes. i have been holding off buying any additional Canon - or other brand - stills imaging gear for more than 2 years now. Already switched from APS-C / mostly EF-S to FF -> EF lenses (L plus non L) plus additionally EOS M with EF-M lenses as a second, smaller system. Now i am just sitting back until i can consolidate everything on one single, compact mirrorless FF system.
Am waiting to see what FF mirrorless system Canon comes up with. Sony has not convinced me enough to switch so far. One of the main reasons are Sony FE lenses. Not compact enough to make switch worthwhile for me in terms of size/weight and also far too expensive - for no gain in IQ compared to the Canon glass I have.
But more generally: no matter whether Canon goes with EF mount or new "slim mount" for their mirrorless FF system, all currently existing EF lenses will be "legacy". They will hopefully and in all likelihood work as well as they currently do *in live view mode on Canon EOS DSLRs. Especially as far as AF performance goes. Only the very few EF lenses with STM or Nano USM drive are basically "mirrorless enabled". All other existing EF lenses are designed for traditional DSLR Phase-AF operation and will not be able to utilize full [AF] potential of mirrorless cameras with on-sensor (DP) AF system.
Aside from AF I can see a whole range of other areas for improvement/additional functionality possible on future Canon mirrorless FF cameras related to lens-body communication and AI in both cameras and lenses. For example things like improved wireless ETTL which will require more advanced distance information coming from lens all the way to advanced, context sensitive IS systems, advanced user interface functionality (eg think of Samsung's "iFunction" button on all its NX system lenses) and whatever else may be implemented in future native mirrorless Canon lenses. Some of it may be firmware and possibly some existing EF lenses [which ones have a chip built in? certainly not the older ones?] can be firmware upgraded to get some of that functionality. But, who knows? Canon will want to sell us new glass, so they'll make sure we have enough incentive to do so want to do so.
in short: I will definitely not buy a new Canon DSLR. I will also not buy any new EF lens, unless a needed one were to fail or be lost/stolen. Until FF mirrorless is sorted out, I will use what i got - which is not bad for my (amateur) use and needs. Ideally there will be a choice of 3 good mirrorless FF systems - Sony, Canon, Nikon to chose the one best for me from. Hopefully soon, my 5D3 plus EF glass sees less and less use due to size, weight, conspicuosness. And if none of those mirrorless FF systems will get me to a compact, decent IQ, decent UI and affordable (non pro) setup, i may really just settle for a small and cheapo crop sensor system - i could live with EOS M system if need be. Bad for Canon, not for me.