Tough call. Personally, I believe that M will (eventually) "do the right thing" with the 861 and G6x in due course, in terms of handling *decoded* MQA on the input side, applying DSP, and outputting renderable MQA on the processor outputs. (That's actually quite a bit of development and testing effort.) I am less confident that M will add an MQA decoder card to the 861 and I feel that the G6x will never get MQA decoding.
Having spoken to some key people at Meridian recently, I know that Meridian was placed at a disadvantage by being the first to release MQA products. The rules on what MQA can be output, in what form, and where, were more restrictive back then and have changed since those first products (SE speakers and 808v6/818v3) were released. For example, AFAIK the TIDAL PC/Mac apps will perform the first stage decode and output a renderable "MQA stream" which can be received by an 818v3.
The problem is complete uncertainty over timescales. It's really clear that M has been working on a *lot* of new products to kick-start its custom install business, so it's understandable that updates to existing products have been dumped down the list of priorities. Perhaps now is a good time to buy a used 861v8, but not a new one? But if you want to buy new, maybe hold off and get a 218 in the interim, perhaps with a used G65.
These are my opinions only and I have no inside knowledge of Meridian roadmaps.