Here's an article where Nintendo said BotW would only need to sell 2m before being profitable.
Obviously Arms didn't cost even a fraction as much as BOTW (I'd bet money on BOTW being Nintendo's most expensive game ever by a decent margin). So yes it should be very profitable at 2.5m sold. Definitely enough to continue the franchise.
Last edited by HyrulianScrolls - on 14 April 2018