It was something I thought of while playing the games.
Sometimes, we get to see NPCs that will sell you items/pokemons. Most notably the Magikarp man in Gen1 and 3, and the Ragecandybar man in Gen2 and 4. There's also a Lavacookie woman in Gen 3.
But how about we have actual merchants in the game? I'm talking about something like the Kecleon merchant in the Mystery Dungeon series. They appear in certain places with random items, and you can buy whatever you want as long as you have space in your bag, and enough money. Also, there's the secret floor operated by a Kirlia where you can buy emergency items and stuff.
Could we have the same thing in the main series? Like, how about an NPC who sells Lemonades on Route 121? Or someone who carries Thunderstones on Route 9? Of course, they would have limits in their stocks, so you can't just buy everything.
But yeah - I'm just saying. Wouldn't it be wonderful if you were stuck somewhere, running low on HP or PP, and there's a merchant with Hyper Potions and Ethers? Gen 5 have doctors/nurses stationed at good places, but hypothetically, let's just ignore them.