It's my understanding that under the WA system, some things still require a doctor's recommendation.
EDIT: A recommendation increases the amount of marijuana or marijuana-based product one can legally possess (strictly speaking, it offers an affirmative defense for people possessing more than the amount authorized by I-502).
These sort of "house call" or "doctor-on-location" weed businesses rely on people trying to get high that day. I find it incredibly hard to believe that they could be sustained by people who want to remain legal while owning more than an ounce of weed (a rather large amount of weed for all but the heaviest users...).
If it is merely a matter of keeping more than an ounce legally, the urgency is all but gone, and with it the advantage of the house-call system.
Also I sure as hell wouldn't start a business based on the current state of medical marijuana in Washington state; the system will likely be gutted and reworked relatively soon. Furthermore states that legalize in the future will likely follow Colorado's example more than Washington's.
I think one of the remaining advantages of medical marijuana in WA and CO is that it is significantly cheaper than recreational, because no tax is applied.
EDIT: A recommendation increases the amount of marijuana or marijuana-based product one can legally possess (strictly speaking, it offers an affirmative defense for people possessing more than the amount authorized by I-502).
Source: http://www.doh.wa.gov/YouandYourFamily/Marijuana/MedicalMari...