Food as fashion has never made a lot of sense to me. Kale is out (no, not really), jackfruit is in, and so on.
But guess what? In Switzerland, the birthplace of fondue, this creamy cheese dish never went out of style, and once you make up a pot for your crew, you will realize why the Swiss never ever considered letting it go the way of the Jell-O mold.
Emmenthal cheese (or, in Switzerland, Emmental) and Gruyere are the two most classic cheeses used in authentic Swiss fondue. Other traditional choices are Comte, Rachlette and Swiss Vacherin, which melts beautifully.
If you want to add different cheeses, do; you need cheeses with flavor, and cheeses with a smooth, creamy melting texture — classically, cow’s milk cheeses made in the Alpine style. Fontina and Jarlsberg are good thoughts too, and very accessible. Talk to your cheesemonger to see what else is an option.