Discuss how to save money.
Interesting idea.
Some random thoughts:
The intake port wouldn't be desirable in humid climates.
Though the air outside in winter is dry, it's also cold. The dryer heater is much less efficient than high efficiency furnaces or newer heat pumps. So while you'd remove the humidity, you'd have to heat the air more.
It'd be very interesting to see a cost analysis of your idea. Though I believe you'd need one for each climate region.
All points to be considered, but the port could be left unattached to an outside source. Those who don't want to make use of outside air wouldn't have to.
so that I can use cold air from the outside for drying.
But then you'd have to heat the air even more, resulting in more electricity use and added wear on your dryer due to longer cycles.
I'm willing to bet that any heat lost from inside your house is probably recovered if you open the dryer as soon as it's done. All the hot air from the dryer is released into your home, as well as the heat still coming off the clothes.