BJR,
I can remember the 2008 Tony Awards as being the first. That was the year when there was only 3 musicals that opened in the season that weren't nominated for Best Musical or Best Revival (A Catered Affair, The Little Mermaid, and Young Frankenstein), and the Tonys put them on in a quick brief trio performance. Then, they included Legally Blonde, Mamma Mia, Jersey Boys and others years later to showcase that Broadway wasn't just New York, it was touring all over.