Good understanding of the basic building blocks of fullstack development. NoSQL/SQL databases, HTTP(S), REST/SOAP, Ajax, HTML/CSS.
A backend technology of your choice(Python + some framework, node.js, Go, Scala, Java EE, RoR - whatever rocks your boat)
As far as architecture goes, you should understand how to best serve the mobile clients in addition to the web front
A frontend FOTM technology of your choice - but most of all the ability to adapt to new frontend gimmicks.
Great communication skills and a sense of humour (optional)