Speaking from my own personal experience, finding random, open world RP in the housing districts is possible, but difficult and unpredictable. With so many houses spread out over so many wards, and no guaranteed activity from FC members, there is a lack of a centralized "spot" for people to gather and mingle randomly on a day to day basis. There is only one Quicksand, one Drowning Wench, so they make for a much easier point of congregation for random open world RP.
Now, walking into an open RP FC house is probably going to be your best bet, and is usually very fun and pleasing for both yourself and whatever FC members may be around. Alternatively, if you wanted to find some random RP on the beaches of Mists, you will probably have a much harder time. Not that these places are not used for RP, but they are usually planned in advance, or utilized primarily by nearby FCs. Unfortunately, in most wards (which are always a mix of RP, PvE, Social, and Abandoned houses), the streets are rather dead with the exception of the occasional passerby.
Now, walking into an open RP FC house is probably going to be your best bet, and is usually very fun and pleasing for both yourself and whatever FC members may be around. Alternatively, if you wanted to find some random RP on the beaches of Mists, you will probably have a much harder time. Not that these places are not used for RP, but they are usually planned in advance, or utilized primarily by nearby FCs. Unfortunately, in most wards (which are always a mix of RP, PvE, Social, and Abandoned houses), the streets are rather dead with the exception of the occasional passerby.