Hi. I bump into this issue several time while working on large aerial views : all textures are reduced to a 4k resolution max, which is really too low this days. I’ve seen other users ask about it around, but it still doesn’t seems to be on the list of future evolution.
I understand that you downscale texture in order to keep the engine working smoothly, but you should add it as an advanced option. Unreal engine, which is your base engine, support easily 8k textures, and Lumion can even go up to 16k, which is very handy when rendering large urban plans.
I think it’s almost nothing on the developer side, as the engine is already able to deal with it, so I hope it 'll soon be added.