I think someone from Holland really should answer this one
I was about to, until I realised that the OP wasn't really asking about Holland...
But now you're asking: In Holland, above 1200', mode-S is mandatory for all powered flight, VFR and IFR. Even non-powered flight needs mode-S in a lot of cases, or be severely restricted in the area of operations. And yes, all ATC Dutch units are mode-S equipped (100% coverage) so they will notice.