I was concerned about that as well. The bulk of the weight is in the two steel bars, and I have aluminum ones to swap them out for is this proves to be too much. The weight on the Z-axis and Y-axis modules is pretty negligible - less than the carriage mounted to the X-axis, and the modules are interchangeable so they should be able to handle the weight easily. The parts together weigh less than the rotary module, though, so I don’t forsee any problems.
I seem to recall a forum thread which had the specs for the linear modules including how much weight they can handle, but could not find it doing a search. I did see this:
weight limit on snapmaker table
…which suggests 4 kg is safe.
When I next disassemble it (today likely) I’ll update this post with the actual weights.