I kept a moluccan python in the same rack as my ball pythons until his display cage was ready, and I now have two freckled pythons that will go into the yearling ball rack after thier quarantine. I personally don't see a problem with housing other species of pythons and even some tropical colubrids, but if your going to add Boas into the mix, be real careful who you purchase your Boas from because even if you quarantine them there is still a chance of the Boas being infected and passing IBD into the collection.
I personally would be cautious about adding boas to the mix, but on the other hand if you are selective about who you buy your boas from you shouldn't have a problem.