This may be stretching the ole brain muscles, but I wouldn't mind seeing mechanics evolve in content that are relevant to the skills you unlock through leveling. Rolling around ideas in mind. An example might be getting your gap closer at [insert level], then the following instance might include a moment when using specifically that may let you narrowly avoid damage. Said moment is repeated once or twice during that expansion's life cycle, keeping it relevant without overstaying its welcome. I dunno. I've been up too long. Might be going nuts.