1. economically/financially/commercially viable
perfectly/truly/extremely viable
consider/regard sth viable
remain sth viable/ make sth viable
prove/sound/seem
2. 中国经济下行，许多O2O模式显得不再可行。
China is experiencing an economic downturn. In this regard, a decent number of O2O mode seem nonviable.
As China's economy is going downhill, many online-to-offline(O2O) business no longer seem ( commercially/economically) viable.
3. 虽然到目的语国家生活是学习外语的一个好方法，但从经济角度上说，却不一定是一个可行的方法。
Living in the country of your target-language is a good way of learning foreign language, but not an economically viable one.
