The impact of the Ban on the 6 Muslim Countries is affecting the housing market in a much broader perspective in places like Silicon Valley where there are a lot of people living and working on H1B and other visas. It is fear of the uncertainty and the mess that is being created with the implementation that is having an impact, not that ban itself.
This fear is preventing potential buyers from buying and locking in favorable mortgage rates that may benefit them for years to come. Most of the high tech buyers are probably not coming from those 6 countries but the fear reverberates throughout places like India and China and visa holders from there who make up a large pool of the workforce here.
I personally know of even Green Card holders being so frightened by this fiasco that they cancelled their Cancun family vacation while kids were out of school (and lost their deposit). These are not visa holders, but the fear out there is that great.
The article below talks about some options and things to consider for people with Visa holders who are concerned.