How will the new lack of SAT subject tests affect admissions?

Since the SAT Subject Tests are no longer available they become less and less relevant in the College Admission process. Some schools like Harvard will accept Subject Tests taken within the past 5 years while 99% of colleges do no care about them. For instance CalTech and the UC schools like UCLA, UC Berkeley and all California State colleges are test blind so even if you have them, they will not be addressed in their admissions process.

Its safe to say that most competitive colleges "null and voided" the requirement as soon as College Board decided to end them as well as the writing portion of the SAT.

If you want to ensure that college admissions officers understand that you have mastered the previous sections of the SAT Subject test, then it would sufficient to submit As on your transcript for grades or 4s or 5s on your AP tests. Now that Subject Tests are no longer given, it's safe to assume that more weight is placed on both AP Grades and AP Tests in lieu of Subject tests.

But remember that almost 95%+ of colleges have no requirement for any standardized tests so if you have a very strong academic narrative with perfect grades, difficult course rigor and evidence of IV/IC intellectual vitality, there is no need for additional standardized tests. While the SAT/ACT help your application if and only if you submit a high score relative to the 50% middle percentage, it's not necessary if you are both a top ranked student and your academic narrative if consistent with other admits from previous cycles.

I think you are over thinking this and recommend that you focus instead on the quality of your ECs, essays, recommendations, interview prep, and any optional videos/portfolio/add'l writing submissions.

Good luck.