Subject pretty much says it all. It's nice that the getRawMetadata() method returns lat/lon for "gps", but it would be great to be able to set the values as well. I've got my plugin reading gps tracklogs, it would be nice to be able to put the data into the photos :-)
It seems like supporting "gpsAltitude" at the same time would make sense, but I'm personally less interrested in that.
In general, if it will be possible to access (read/write) all EXIF tags with its name will be good. Also true for IPTC/IIM tags.
Maybe, what someone can do with Geo-Tagging, this external program can give some very good ideas: http://www.geosetter.de
A simple LUA scripts, which also uses the Exiftool can be found here:
But if sometimes LR will have functionalities like GeoSetter, this will be the best solution. Maybe, in a few years, every camera will have built-in GPS hardware, but if you look at GeoSetter, there is much more in Geo-Tagging than a GPS coordinate. I prefer, to have only one tool in my Workflow... And I like to see LR here. ;-)