A full suspension might be great for pure off-road, singletrack, rough touring. Although Adventure Cycling recommends a hard tail mountain bike with suspension fork for its Great Divide route. Probably due to the numerous miles of gravel and dirt roads and the extra reliability of hard tails and simple elastomer forks over oil/air forks on the full suspension bike or higher end forks.
For riding on the road, where most tours take place, suspension is not necessary. It slows you down because it takes energy to squish those coils/struts/forks/etc. together. Energy better used to get you up the mountain or to your campsite against a headwind. Most people who use hard tail mountain bikes for touring put on skinny, slick, high pressure tires to reduce rolling resistance compared to lugged mountain bike tires.
I think if you are touring loaded, the urge to ride a loaded bike through or across anything will be seriously diminished. When you have 50 pounds of stuff on your bike, or pulling a trailer with 50 pounds piled on it, you quickly learn to avoid riding through or across anything without considerable thought. One reason is a loaded bike or one pulling a trailer is not very maneuverable. You don't just power over things or quickly swerve around them.
My suggestion would be to try a 2-3 day tour with the full suspension mountain bike and see if it works for you. The extra effort required may not matter much to you. Getting a new official road touring bike is easy if you have the money. There are many that work very well.