zookozcash

Here are current stats about shielded and unshielded transactions in the last hour/day/week/month:

https://explorer.zcha.in/statistics/usage

And here historical stats about shielded and unshielded transactions in the most recent 100 blocks over the life of the blockchain so far (about 6 months):

https://explorer.zcha.in/statistics/timeseries?supply=false&...

Note that a big part of the shielded transactions is because coinbases are required by the consensus rules to be shielded when first spent. This was in order to provide a guaranteed privacy-set. If you make a shielded Zcash transaction today there is actually a very large privacy-set of possible previous transactions which could be inputs to your transaction.

In the long run we intend to improve the functionality of Zcash shielded addresses and to deprecate Zcash transparent addresses, so that all transactions are shielded and so that the user experience is simpler.

It is not true that this result was previously known. Please see the section “Comparison with related work on Monero linkability.” in the paper (https://monerolink.com), which starts "We note that earlier reports from Monero Research Labs(MRL-0001 [10] and MRL-0004 [7]) have previously discussed concerns about such deduction, called a “chain-reaction,” based on similar insights as described above. However, our results paint a strikingly different picture than these." and then goes on to show those striking differences in the new results and the previous knowledge.