Went to one of the exam venue where HSK exam is conducted in Malaysia. I spoke with the HSK examiners about the standard of HSK vs SPM Mandarin.
1. HSK is different with SPM Mandarin. Mandarin subjects in Malaysia Chinese school cover the Chinese literature and classical Chinese.
2. There is zero literature content in HSK syllabus. HSK primary focus is on the application and usage. It is like the " second language subject " for people whose mother tongue is not Mandarin.
3. The standard of SPM Mandarin is on par with the highest level of HSK (HSK level 6), if not beyond.
and yes, it is getting more and more popular as an assessment for Mandarin proficiency for foreigners who wish to demonstrate that they have learned Mandarin.