Let me tell you what the problem is?
I can always add extra columns in the csv file and add this information to the kml. So far so good, but if now support for NeXML has to be provided, I should know the exact format of the NeXML data. It is important to note that both the csv file and the nwk file have to replaced by a single NeXML file. From the NeXML Manual page I got to know how a basic nwk file will be represented in NeXML format. I used the online converter from newick->nexml which can be found here. nexml.org.
Meanwhile, I have received my welcome package from google but there's some mistake in my name on the card. So bit of extra work here. :P