The ball wasn't always red, the kit wasn't always white, the bat wasn't always flat, the ball wasn't always bowled over arm, there weren't always three wickets, and so on. And every time these changes were made the cricket viewing public was up in arms (none so much as the change to over arm bowling - it was nothing short of blasphemy!) and yet these changes are now all part of "traditional cricket".
In short, this will become part of the evolution of the game and in 5, 10, 20 or even 30 years it will be "traditional cricket".
Timeless tests were stopped for organisational and economic reasons, the introduction of day/night tests will be for the same reasons. So, insomuch as things change they ultimately stay the same.