This is the first I've heard of Plurk, but there's an API and even basic Python example code. It appears a few people started Pidgin plugins for Plurk, but I didn't notice any that progressed much beyond establishing a project space.

Without really looking at the API, I'm going to guess that, yes, someone could make a Plurk client for Maemo 5. If you've ever considered learning Python, this might be a good opportunity.