Emulating ITTY-Autostart protocol is eminently reasonable. 

Some of us have machines that power up/down in autostart mode so idling with diddles for minutes between messages would just run the machines unnecessarily. Constant mark is probably OK. Many (most) TUs have mark-hold when there is no audio signal. 

That Heathkit must be a marginal design. I’m really surprised. Hard to imagine a proper TU being harmed by being constantly on mark. My Dovetron has been on 24/7 for at least five or six years. I just turn on computer audio when I want to print something. Otherwise the loop is in mark-hold. 

My zwei pfennigs worth. 

Nick