I don't think there will be a big push for 4k until broadcast heads in that direction. Regardless, I'm pretty sure that they can update the software to support 4k and bluetooth 4.2. The new Apple TV has the HDMI 1.4 spec which supports 4k. Additionally, 4k streaming eats a lot of bandwidth. The iPhone 6 had its bluetooth firmware upgraded to 4.2 when iOS 9 was released. All of this is speculation of course, however, I have a feeling there won't be a hardware upgrade for at least 2 years.
I agree, I don't see the point in people holding off for v5 as it's likely going to be in 2 years or so. 4K would be nice, but there is no real reason to push having this feature in current devices as we are 3-4 years minimum away from major exposure to a large amount of 4K content. By that time you will need to purchase a new device to work with it anyway.
This version of the Apple TV is a great start in the right direction of where entertainment devices in the home are going. It is effectively a fully fledged entertainment device and once the App store gets up and running, we will see how powerful a device it is.
For the money they are asking, I think it's a great device potentially. Although I will hold off for a few months anyway to see what happens first and foremost.