Without knowing the economics of operating an EMB-195 (often times stretching an aircraft comes with performance penalties - ie, the A-321 and B-737-900ER, which take performance hits vs. a B-757-200, despite similar cabin sizes), scope is likely an issue. If 195's are @ mainline but 170's and even 175's contracted out, the cost savings of the common type, common parts inventory, and economies of scale are squandered away. Why get 195's @ mainline now when you can strong-arm your pilots into give-backs in contract talks, plus strong-arm your contractors in the future into acquiring them on their balance sheets, perhaps where they take on more of the revenue risk too (no more 'cost plus' or 'fee for departure' contracts)?

If the 195 is a good platform to operate, it seems we'll see them in the US domestic market after the pilots of UA/CO, DL, AA, and US get their new contracts, helping solidify the certificate placement of these kinds of aircraft in the future.