WFS client is NOT implemented in any of the Web APIs yet, and the road map to have it in near future is still not clear. So you probably have to extend the existing framework to support it for now. But we would like to hear more request like this to adjust the business justification to add WFS in Web APIs, so if possible communicate the idea through http://ideas.arcgis.com, or even directly to Web API teams in user conference or dev summit.
