Let me declare at the outset that I was not in favour of the mandatory introduction of mode S.
However, whilst I am “happy” to rely on existing services and my own eyes to hopefully spot traffic in VMC outside of CAS I am conscious that with new and more capable aircraft becoming available it is possible there will be more pilots operating in IMC outside of CAS. It is in this respect I have a problem.
Aircraft operating in IMC are required to be equipped with at least mode C and presumably the majority will convert to mode S. However it has become increasingly apparent to me that there are a good many pilots who are prepared to operate in conditions that are either IMC or very close to, who are either not instrument rated or are not operating suitably equipped aircraft or both. This will include those who decide to nip through a gap in the clouds to get on top, but find themselves in IMC for short periods, those that fly very close beneath or above a cloud layer and those that fly when conditions whilst not IMC are as near as you can get. The fact that these pilots are not instrument rated, not flying in suitable equipped aircraft and breaking the law is all irrelevant for those that are on an IFR flight and come into conflict with them.
I suppose in the same way that many certified aircraft are fitted with far better avionics it is also the case that so are many home builts, and non certified or non IFR compliant aircraft. Of course this in turn gives the “operators” the confidence to fly in more marginal conditions.