I am curious how this plays out. To be honest, I never used used the Las Vegas Loop when I lived there as I never really had a need to go to the convention center.
The last mass transit idea in Las Vegas, the Monorail, essentially flopped. It doesn't go anywhere useful for residents, and it is too far off the strip (the resort corridor) to be useful for visitors and hotel guests. It might have had use if it connected to the airport, though I think the taxi lobby may push back on that. Personally, I think the Monorail should have been built right down the center of Las Vegas Boulevard (the strip) with large windows, with a connection to McCarran Airport (or Harry Reid Airport, if you will).
An underground tunnel would not have the same sights. But if Boring Co connects it to something useful, like say, the airport, it might succeed.