The 100A is tight because of clothes dryer, heat pump, bathroom heater etc. The house is a bit undersized. Also wife has expressed interest in induction cooking range. A car charger is also highly desired but I realize that is outside the budget. I am trying to exclusively run the range and clothes dryer by relying on such a device. They would run on separate circuits to the panel. But if the panel is oversubscribed to the service line then I want to ensure that only one of those breakers is turned on.

I am not aware of a device such as what you are describing. I could whip one up myself with some amount of effort (i.e. find a high-current contactor and marry it to a microcontroller). But that doesn't really help you much.

While many houses are just fine with 100A service, you happen to have several very power-hungry appliances, and you are planning to add more. Some amount of oversubscription isn't necessarily a problem. Breakers don't trip immediately, if you only exceed the power budget by a small percentage. And the appliance manufacturer always gives you worst-case numbers for power usage. In practice, none of your appliances pull the full amount all the time. That's why 100A is fine for many households, and why you might still be OK for now.

Have you actually seen breakers tripping? You might want to ask an electrician to do a proper load calculation to give you a better sense of just how close to the edge you are living. Your range and your dryer are probably OK by themselves. But turn on any of the other power hogs and that's it. Also, don't even think about an electric car.

So, even if you are fine right now, you will need to upgrade your service panel sooner or later. Everything else is a bandaid solution that is just going to push out the inevitable for a year or so.

We upgraded our service panel a couple of years ago. It wasn't trivial. But it also wasn't as bad as I would have expected.

So your solution of running the drier at night will make charging your car a similar problem in the future once a week. Night is the preferred time for car charging. If you switch to a gas drier your problems are gone until you get the new car.. Otherwise a change to a 200A box is another route. I don't see moving your house wiring over will be very difficult or expensive. You won't need to replace any house wiring except likely the main supply line from the meter to the new box. Take a picture of the current wiring layout with the cover removed. Label each wire run. Print out the picture. Square D QO makes good boxes/breakers. Adding a 50A circuit and outlet for car charging at the same time would be economical.

You need an electrical upgrade. Period. Do not stop. Do not pass go. Do not waste $200+++ on an joke workaround to inadequacy.

This is not optional. Make it so. You may even need the service drop upgrade with your future plans. Or you may can just add a new panel and use the old as a sub panel. But. Only do this once. With the future in mind.

Yes, this is possible to do, using a selector switch as commonly used in industrial applications. Schneider makes a wide range of these types of switches. Visit an electrical supply house and see what they can get. You'll have to install in a separate enclosure near your panel. These switches can be purchased to cut power off to one device before powering up the other. Watch the size of the induction range. Our cooktop takes a 50a breaker!