There were two interesting items in this article.

The first was:
Stereophile readers can find out about upgrading 861 reference v1-4 by emailing stereophile@Meridian.co.uk

I thought the upgrade program had ended

The second was:
Some older modular boards still compatible

I know that there has been some reference on the forum to older boards working but is this now official?

861v8+ID41 Revelation One filter, HD621, Musical Fidelity M8 700 mono blocks, Focal Scala (x2), Focal Mini Utopia (x3), Velodyne DD18, Oppo BD105, Roon NUC, 218, Radiance 2021, JVC X9000