So this can be a somewhat tricky question depending on the streaming format being used (H264, H265 or MJPEG) and then the bitrate and resolution selected, CBR vs VBR, etc....
So to boil this down to it's simplest form we'll assume we're going to max the bitrate of the camera out using H264 (8192kbps)
Then we need to look at the backplane capabilities of the gig switch... the Dell Power Connect 6248P switches we use in house have a 10Gb backplane.
IF we had enough of the switches and enough cameras on hand we would be able to max the switches out with about 1,280 cameras; general network rules of thumb obviously suggest to never consume 100% of your available bandwidth but I think you get the idea.
As long as the backplane is big enough you'll be able to handle loads of cameras.