We've forgotten about those guys, right? The NPCs that used to be invaluable for selling us players tools, weapons, and such? Somewhere along the line, the game changed and players took control of mercantile matters into their own hands. Only a handful of shopkeepers have anything worth buying, and even fewer are worth selling to. This goes double for any shopkeepers that use a currency other than gold.
The cause is simple enough: they're all stuck in 2006, with many selling items that every player has permanently attached to their toolbelts. That's not to say that their wares can't be updated to fit a more modern game, even without thinking outside the box.
The simplest option is already in game. Some shops offer unique resources, essentially turning them into an effective daily moneymaker or training method, especially considering how many hard-to-get resources the average player will need to reach any significant levels. Gathering skills, on the other hand, could benefit from consumable items that temporarily increase yield or experience, or perhaps automatically bank your items—assuming they can be balanced so that they aren't just a poor man's aura or sign.
Another option is to make them worth selling to. The precedent for this is already there as well, in the form of daily challenge rewards and, like both it and the above, it could be limited to a certain amount per day. This sort of thing also wouldn't be hard to work into the game's lore: many items relate to combat, and the current story arc involved a global war. Of course, players shouldn't be completely reimbursed as they are with daily challenges, but even a small daily boost may be enough to take the edge off of a lot of more expensive skills.
Finally, a number of shops could sell cosmetic items. Many already do, in-game: the desert sets were always popular in the old days, but almost none of those items have aged well. If inflation is an issue, some higher-class items could exist as gold sinks, similar to how the Keldagrim stonemason sold such items for player-owned houses. Unlike in the past, though, pretty-but-useless items can be made usable through keepsake keys, rather than just being something you wore when you were doing nothing (something players stopped doing a few years back).
Items with an actual use, on the other hand, are now almost exclusively the product of bosses and high-end skills. That's not to say that those that already exist can't have their prices modified to be more in-line with their current place in the game, or that high-end items can't continue to have components bought from shops. If items that degrade are going to remain the standard, they could even be repaired through store-bought items rather than with gold: that kind of thing could even be a cheaper, high-skill alternative to having them repaired in Lumbridge.
It's just a shame to see something that was once an integral part of the game's infrastructure go to waste, especially as a result of neglect. We could very well be sitting on the solution to a number of skilling problems, and all we have to do is clean the dust off.