Yes and no. Only so many routes/frequencies will be suitable for <76-seaters and regionals will be hamstrung in the future of not having enough F/O's in the pipeline. The ability to get pilots and higher yield economics of > 76-seats will bolster mainline over regional in the future. That being said 64 and 76-seat RJ's will still have a significant role and the AA network will have hundreds of them, again spread out among 3-4 carriers.

Just my .02.