Not exactly sure what you mean (despite the dictionary meaning), but here's my best guess.
You surely can include presence information in your mashups at any time, the construction of EMML or mashups don't restrict you in any way. The only limitation is that of ideas to build it :) And of course, a service that provides presence info.
As an example- Let's say I want to build a "What am I doing" widget for my blog, where anyone who comes to the blog knows what's up with me, with the option to research that particular activity I'm doing. Here's a mock -
http://www.freewebs.com/threepointone/img/mash.png
[it's not letting me show you the image here for some reason, but that's the link]
So importantly, I'm using 3 services:
1. for presence, Twitter (has a well documented api, REST format)
2. YahooSearch (also has a REST based service)
3. Yahoo's Term Extraction service to pull keywords out of the presence message.
MASH IT! Pull the data, and show it, while simultaneously pulling out important terms using the term extraction service and doing a yahoo search on it and displaying results. The EMML shouldn't be too tough to build, you could probably do it in wires itself. And the mashlet should be simple too.
Maybe you wanted online status presence on your gtalk? Surely there's a service/api for that. GPS location that your're broadcasting? Go for it.
I hope this answers your question on presence.
1: the fact or condition of being present
2: one that is present: as a: the actual person or thing that is present b: something present of a visible or concrete nature
When will I be able to include presense information in my mashups?