Gold is not always going to go up in price, in fact it's going to be going down after this current bubble pops. You might want to look up 1979.
Trump wants the gold coin to be over 3 inches in width, so we're not exactly talking 1 oz pieces. They'll be sold at double or more spot price, and, well, I am not quite sure how many you're going to be able to buy, especially given the limited mintage and as dealers buy most of them to resell as graded slabs at ridiculously marked up prices.
Modern commemorative gold pieces, due to their already high prices, don't increase percentage-wise in value as much as silver or base metal coins. A $10,000 piece, no matter how low the vintage, is not going to double or triple in value over time. Even with a fan base like Trump's, they're not exactly much prone to be the coin collector/investor type.