@Rusalka There is no limit on the number of contents that a room or other container may have.
There is no hard number limit on LCON() per se but remember that you're still limited by the size of the MUSH's buffer. If your MUSH has a 4k buffer (4096 bytes, or characters, in length) then LCON() would be able to return a string up to 4095 characters in length. That's a lot of dbref#s
There are various ways around the buffer limit, the XCON() function, for example.