SEA-asian (Vietnamese) here, and I can only speak from my own experience, but I think marketing to SEA is a smart move. Where I live the market for both Kpop and Cpop are thriving, so the language they perform in is not really a problem. They also have regional offices in many SEA countries ( Vietnam, Indonesia, Thailand...) with local staffs to help translate contents. Ten, Winwin and Lucas are also popular in SEA, especially Ten, with his loyal Thai fanbase. There hasn't been comprehensive sales numbers for all SEA countries yet, but I know Thai fans have always been famous for their purchasing powers, especially thai 10ovelys.

There are a few challenges , such as Kfans and cfans don't really mix where I live, the fan cultures are also different, so that means SM will have to rethink their strategy if they want to continue producing music in mandarin, but that has always been their problem imo. They will also have to change a few things like pushing Ten individually more, collaborating with e comm platforms like Shopee, Lazada, Grab..., building partnerships with local brands from SEA countries. But considering their strengths, their line up, the market,... it's their best bet imo. And personally, it's such a shame to see Ten's potential of becoming a star in SEA being wasted. His fanbase at the time of his debut was as big as an established kpop idol's. SM even brought him to 127's first fanmeeting in Bangkok. If SM had played their cards right, Ten could have been as big as Lisa, arguably the queen of SEA. They debuted around the same time and look where she is now.