Yeah, sounded good at first but the more I think about it the less I like it.
- As a temporary game mode, progress in leagues is much faster. If people will get to know the new skill at these faster xp rates, they will be disappointed when the skill releases. If there's no xp boost, that would probably mean you'd need to spend 100s of hours to max that skill...
- Either they spend a lot of dev time fleshing out the skill really well, which runs the risk of a lot of wasted dev time. Or they don't work it out well and then players might not like it because of that.
- Imo training a skill is not something you do from 1 to 99 as a single goal. For me the whole fun in rs is to constantly switch up what I'm doing. A skill can be good, but if it's so central to the game mode it's still very likely that you'll get bored of it. Except for combat I can't think of a single skill in RS that would be exciting as a central theme to the league, without significantly altering it.