Hello!
An online Gym League is something we've actually tried before, both through Netbattle back when Gen III was out and in WiFi when Diamond and Pearl first came out. Whilst it does sound really interesting and everything, we found that in both cases once the initial buzz wore off, it just stagnated and became more of a pain than anything; different time zones meant people lost interest once it became harder to get the battles going.
We did have plans to resurrect it actually, but nothing came of that once we'd passed it onto the members who wanted to make it work again..
If the demand is there, I'd have no problem overlooking this but at the moment, I'd say from history it's just one of those features we've tried to do that initially sounds fantastic and then people get bored of it too quickly.