I totally agree with you. You can change lenses in all other modes, but not for 4k60fps and 8k24fps. All you can do is to pick the lens before recording and thats it. It's a big pitty and shame for samsung that this is not doable here.
Just contacted Samsung support in Poland. They don't know when the future will be introduced nor have any idea about even high level plans of such implementation. In other words, they don't care and it might be that they will never introduce it. What is very funny, they've said that they will register this as a suggestion. When I asked for the ref no. of this case, they said suggestions are not registered against any numbers or tickets :) I don't even know if this was registered at all. If they don't assign any ref numbers, how can they be sure about any trends or customer needs? How they know on what they should work next, to satisfy customer needs?
If they are concerned about overheating, then why recording works indefinitely on all the lenses separately? Switching between them should not generate such a great computing power consumption to cause overheating. Especially if this works for all the other modes. But if this is the case, then I agree time limitation or other means to mitigate would be good.
Samsung, as a customer, I'm very disappointed. Not only with lack of such basic feature, but also with the customer support you provide.