Theres been no official announcement and no official ETA
A lot of rumors about a 4K ready box being released later this year, but VM play their cards VERY close to their chest until anything goes live.
Put it this way. Like you say the competition have launched them a while ago...VM basically HAVE to step up sometime soon.
Although I would say, with the dearth of 4K content available (anywhere) its a cart before the horse situation with the suppliers that have launched. And just to put the tin lid on it 4K displays are already out of date- HDR or ULTRA 4K is the new standard.