The first question I had when I saw the term was: what illnesses are they including in the concept of "IACCs"? If you take a look at Table 1
in Solve's paper, you see the list: Long COVID/PASC, ME/CFS, fibromyalgia, post-treatment Lyme, POTS, MCAS, EDS and GWI.
The first problem is that what these conditions have in common isn't that they're infection-associated (fibromyalgia isn't, EDS either refers to one of a number of Mendelian connective tissue disorders or the type III polygenic hypermobility, no real evidence for the nature of the trigger in GWI, many cases of ME/CFS aren't infection-associated). They're not suggesting an institute that would include, say, Guillain-Barré syndrome and reactive arthritis - both are "infection-associated" but no-one would think of grouping them together in a similar way let alone grouping them with ME/CFS, fibromyalgia, etc. In fact the only thing the conditions on Solve's list of "IACCs" all have in common is that they're poorly understood or defined & sometimes psychosomatised.
I think it's counterproductive firstly because there are many "infection-associated" conditions where the link to infection isn't at all the most interesting or salient feature, and also because we've been trying to define ME/CFS quite narrowly, around the concept of post-exertional malaise & so forth and Solve are working against that by trying to lump ME/CFS into a broad category containing a wide variety of often poorly defined syndromes encompassing all manner of unexplained symptoms.
I suspect there may have been political reasons for introducing this concept (trying to establish a link to COVID and the increased funding for infectious disease research) but it's not very well thought through.