For preservation? No, not really. The only use for preservation I think makes sense is, for example, if you only have part of the data in the question, but most of it is lost media; and even then, it's not really ethical without permission from the original creator, and if the original data is lost, then it's likely the original creator can't be easily reached anyways.
It's not really "preservation" to say, use AI to make a brand new voicebank out of old sample data, when that old sample data is still available in its original form. If its original form is still accessible - then it's already preserved. I think it makes sense if ( again, keeping consent in mind ) you only have partial material available, and you want to use AI to restore it as best as it can, and try and make at least a rough approximation of the missing original material, just so there's something that resembles that missing material available. But it's not "preservation" to use AI to, say upgrade an older voicebank to a more modern standard. Generally speaking, that's just a whole new separate product as long as the original is still around.
I think it's fine if people want to do that with their voicebanks ( again, CONSENSUALLY, cannot possibly stress that enough ), but I think claiming it as "preservation" of vocal-synths comes across as a bit dishonest if it's not something like the very specific aforementioned scenario, and even in that case the ethics of it can be very dubious.