If today, some inventor demonstrated a $25 device that showed you all traffic of concern that you could velcro to the top of the panel and run on a battery good for 50 years, it would take ICAO and the various CAA's upwards of 15 years to certify and mandate it
It's not that cheap, in Italy it's sold for €575 + vat for the basic model, anyway since there is still an open debate on whether both system should see and talk to each other, while profitability and competition seems to play a higher role then safety, it might take even longer for the various CAA to approve it as a mandatory equipment, as the basic rule of thumb says, if you can't see and avoid, don't fly vfr, isn't it? (Even if we all sometime had breached VFR just for a little bit and nothing ever happened, but as flight safety might say, even a small breach could mean a not broken link to the chain that leads to an accident,,,)