In hindsight this seems like a really obvious question now (laugh), but I think it’s really interesting that Elsecallers can travel to other planets too–we didn’t know that before.
There are hints in the names on the map of Shadesmar.
Since getting this answer I found out a few more things about this on the 17th Shard. It looks like previous WoB confirmed that there are hints in the names of things on Shadesmar somewhat related to Worldhopping, and we also know that the Expanse of the Densities is a planet that we already know. He could be alluding to those tidbits with this answer, who knows.
If you are viewing this on github.io, you can see that this site is open source. Please do not try to improve this page. It is auto-generated by a python script. If you have suggestions for improvements, please start a discussion on the github repo or the Discord.