Not gonna happen. It takes the fun out of... actually, it doesn't harm trading. You can't trade in one Game Card... I don't see why they don't do this?
Okayyy!!!Let me get out my economics book :D ::flips through pages in head::: Put it this way, pokemon games are a utility and with all utilities you may want it (or need) or just want some updates to it (like more saved files). These saved files are marginal utility (you buy/have more thus making you happy) but like Bleu pointed out pokemon games are slow and sooner or later you'd get tired of playing through another saved file (law of diminishing marginal utility)...Now if Nintendo adds in more saved files we all may be shortly happy..but sooner or later the LoDMU will come into effect an more saved files would just mean less fun and possibly more headaches...that means you'd be less likely to buy another pokemon game since you already have more than one saved file on one..and you've gotten tired of it already :D. And one thing we know about Nintendo is that they want you to buy more pokemon games.
does that help? And a sidenote..like I mentioned in another post Idk how much the DS catridges can hold so more saved files could mean limited capabilities in other aspects (graphics, etc).