Um...not sure if anybody actually tested this, but I just have been doing so. It doesn't work...well, it doesn't work like it should. The new variables, of which the most important one is #Sender# (and maybe #Recipient#), simply just echo what you have the affected List's "List To Address" and "List From" address set to. So, if I have a list called test@test.com, and have its settings set to "from" address is the List Address (which you *HAVE* to do for dmarc, etc), no matter what email address I send a message to the list from, that variable is always simply, "test@test.com" ...which, sure, is the "from" address, but obviously does not add any functionality whatsoever. I mean, if I send a message to test@test.com, from test@abc.com (and test@abc.com is on the list), then the #Sender#, one would expect, would be, um, you know, test@abc.com. Nope, its test@test.com ...
...so, basically, this new feature is useless since for most lists (which have outside email addresses) you have to use the list address as the from address, this does not, still, display the actual sender of the email.