I'll say this again another way – if you need an EF lens to get work done or don't expect to buy an R body for a while, then of course, the the fate of the EF line means less to you. But if you shoot for personal pleasure or are a pro and don't necessarily need an EF lens right away, waiting would be the prudent thing to do. The resale value of used EF lenses is going to be on a downward curve effective immediately. And if you're even remotely thinking of going all-R, then dump your EF while the resale is still decent (or don't care and keep it forever).
Keep in mind that one thing hurting the EF mount is Canon has yet to release an EF-mount body with a stellar full frame sensor. Sure, the 5D4 hangs on to the edge of acceptable, but we all know where it stands in relation to some of the competition. If the 5DsR II or 5D5 is an EF camera, then we can all put down our umbrellas because the sky won't be falling. But I don't think that will happen.