I see speculation every once in awhile about possibly re-engining CRJ-700s to make them more competitive vs. ERJ-175s. However, doing so might make them too heavy for scope in a 70 seat configuration (just like the 175-E2s). It might induce problems with weight and balance too. But in a 50 seat configuration, re-engining with heavier engines that are 20-30% more efficient but still under scope MTOW might actually be feasible. If UAL has some success with the configuration on used aircraft it will be interesting to see what happens down the road.