You think the RJ flying will die down or both will have lots of flying but movement is better on the 175?
I think for anyone getting hired on in the CRJ or 175 today will have near equal opportunity of advancement in the first 2 years with the company seniority wise / bidding power as an FO. The CRJ and the 175 are both being stacked somewhat evenly so progression on one or the other won't be overly noticeable in a 2 year period for a person being hired today. Most guys who are currently CRJ FOs aren't going to transition to the E-175 as an FO. The CRJ FOs are looking to upgrade and move on. So even though the E-175 may be more senior as an FO overall, where you are on the seniority list coming in today it won't matter so much. Your progression I think will be fairly even for a CRJ and 175 guy getting hired today. Once you've been here 2-3 years upgrade is imminent, and then you can choose between upgrading to the more senior 175 or the more junior CRJ. If the music slows or stops, then at that point you can consider transition to CRJ FO or stay as a 175 FO after 2 years if upgrade is not imminent. The CRJ is definitely a more junior aircraft when it comes to upgrade there is no doubt about that. So if we say the 175 and CRJ are equal seniority wise for a new FO, then now you're looking at the type of flying. Senior FOs will take more of the 700/900 flying, and you'll be left to fly the 200. The difference in 175 trips at 200 trips is pretty big. The 200 does more Brasilia type routes while the 175 is doing more mainline type routes.
So now it depends on what base you want. If you have your heart set on a certain base then as an FO the CRJ in some instances may be better.
If you want PHX, TUS, COS, DTW, SLC or MSP I would recommend the CRJ (obviously these are CRJ only bases).
If you want SFO, LAX, SEA, PDX, ORD, or DEN I would recommend the 175 as more flying is headed that direction in those bases, and in some cases the CRJ is being downsized in some bases and removed in other of those bases and you'll have better trips overall on the 175 in these bases.
This is all my opinion. Each guy is going to have their own opinion on the matter. This is mine from the eyes of as if I was a perspective newhire. A year or even 6 months ago I would've recommended the CRJ, but now the 175 is really a much larger presence at the company than it was 6 months ago and that presence is only growing.
To answer your original question, the CRJ flying isn't going away, but the 175 is becoming a more equal presence in numbers. Movement I don't think is necessarily better for a newhire on the 175, but I think for a newhire movement in the CRJ and the 175 overall is equal for the most part for the first 2 years.