The "unverified" status of a Mode C transponding target doesn't affect the usefulness of the return for TCAS purposes.
Also, the verification process appears to be a mere formality most of the time anyway. It's sole purpose seems to be to pick up transponders whose altitude encoder is duff. I do wonder what the point of this verification is, because I could be legally flying under the LTMA at 2400ft, non-radio, with a transponder returning FL150, causing everybody to !!!!! themselves, but they have no means of checking because they don't know who (if anybody) he is talking to. And a lot of people fly OCAS non-radio (with a listening watch, say) with Mode C. I often do just that, but then my transponder (both KT76C and the later GTX330) permanently display the FL being returned on the LCD display. Doesn't almost every Mode C unit do that?
Robin
Hard to say what EASA will do. They are making encouraging noises about deregulating "VFR GA". What concerns many pilots is what tradeoffs will be done to placate the objecting committee members. Screwing IFR GA traffic is one possibility. I understand this may not be directly relevant to you but as I've said I don't think VFR GA is really seriously threatened in the long term; as a sport it will always carry on. There might be increasing problems getting one's certified spamcan maintained but for VFR flight there is the "PFA" type route and this looks like it will be widened; in fact the permit scene is well on the way to pushing out the CofA stuff as it is.