I wouldn't hold my breath for an ESPN 4K channel anytime soon. Even ignoring their financial difficulties from cord cutting (since they lose about $8 per cord cutter, far more than other channels) ESPN/ABC hasn't done a single 4K broadcast yet. Meanwhile Fox, NBC and CBS have been doing events for around two years now. I have to think there's a pretty good sized learning curve for them, and ESPN isn't going to be able to just go straight from nothing to a channel. They'd have to do some 4K games here and there for at least a year, perhaps more, before they were ready.
Though to be honest I think they're probably more worried about getting ESPN+ running well since they will make money off it. 4K will only cost them money, it isn't going to make them a penny, so I can't imagine it is a high priority for them.