I have several bitizens taking up valuable apartment space. Their dream jobs are Chiss HSP and Kashyyk Shack (which can't be built "yet"). Should I keep them or boot them out the airlock?
The answer depends upon your plans and needs.
If you have an immediate need for bitizens to fill other slots, boot them. More will come, they always do.
If you do not need the slots, keep them, especially if they are level 8 or 9 in a skill that you have a job opening for.
Keep in mind, if you have a level 8 or 9, you can put them to work elsewhere until you get their dream level or someone more qualified comes along (i.e. a dream jobber for that job).
More residential spaces are always coming when you can afford to build them.