Barbarian fishing would be cool addition to skilling, also I know they arent neccessary but Monkfish would add a little variety to fishing idk. Maybe make Iron ore nodes have multiple ores instead of just 1 coal maybe a chance of getting 2 at higher mining levels, I know this might be a big change for people going for/ already at 200m xp but even if its only once you reach 99 mining i think it would be a nice addition. I honestly think iron should have less items in shops too, just the availibility of proselyte take away from the challenge and I know that'd mean you 'd have to make it a drop somewhere but yea lol. I'll probably have more suggestions as I play more so I'll return to share =]
Addition: I also think maybe some title rewards based on your overall/single skill xp would be neat. Maybe not in chat but on hover interface possibly.