I now have a subscription to ExpertFlyer and use their alerts in two ways. First, they do offer an aircraft alert, so if there is an equipment change on the flight you are tracking you'll be notified.
I've also kind of reverse engineered one of their other alerts. I use the seat alert feature and go in an specifically select the seat that I am located IN. If suddenly that seat opens up, it means I'm no longer seated in it either due to an upgrade, a reshuffle or an equipment change.
I have long used EF for aircraft change alerts, as they often will not notify you - or will do so too late for you to do much about it. The second idea is brilliant, and I will start doing that, too. It is a shame that you have to babysit your reservations like this, but I have learned that you just have to.