You can actually do this right now, though I'll talk to the team about adding ways of doing it a bit more elegantly. 

If you use the "For Each File" activity, you can target a specific local file by doing the following: 

(of course, you'd probably want to use tokens instead of C:\TestFolder and MyTestFile.txt). 

In the email activity, you can attach these local files by doing the following: 

Note that I selected "File" from "Attachment type" instead of the default "Entry".

I should point out though that this could result in sending multiple emails, each with a different file, if the "For Each File" activity gathers more than one file. For example, if you put in "*.txt" under "Only include files like:", then it will send one email with a different .txt file for each .txt file you have. This can be resolved with some creative usage of conditionals inside your "For Each File" activity, or with more careful management of the file names used in the activity configuration (for example, by not using wildcards). However, I'll discuss more convenient implementations with the team to see if we can come up with a more robust way to send a single file (or the ability to send a batch of local file attachments).