Of the points mentioned above, two are related to the chain and I don't think they have anything to do with it directly. A silent payment will be seen on the chain just like another, the magic happens in the wallet of the person who creates the transaction and the person who receives it. Scanning the chain in search of a silent payment must involve an additional load in time, although today those calculations are done in less than a second. The point where you deal with the age of a wallet is the one that I think can be the most complicated, I would have to do a test in cake wallet; but let's say that you have several payments on the chain and then you receive a silent payment, it would be easy in that case; but if the first thing was a silent payment, when should I scan? Here I think the best thing would be to establish a time window, since it is a new functionality, you can define an initial date on which it began to be used and scan from there.