An ERL with a PoE switch would be awesome, although the biggest thing I'd like is more raw power and still a fanless design. If QoS could be done in hardware that'd be fantastic too, but with all the recent developments there (fq_codel and cake) and the lead time required to bake these into silicon having a more powerful general-purpose CPU gives you more flexibility.
Unclear what the future for the ERL is now that the USG is out. I certainly like the flexibility of a fully customizable router, and having the ERL's hardware evolve into a more enthusiast's box (possibly consolidating with the ERX or the PoE variant) would make a lot of sense.