I have listened to the Purple Album maybe twice, didn't find it as bad as I feared but it didn't leave me wanting more.
But with all these retirement announcements, I'm thinking why they make it final? I mean when you've done music for your whole life what are you going to do now when you're retired? Never ever touch an instrument, never ever sing a note again in public or on record? I don't believe it! So just say that you take it slow and when you do something you do it and when not then not. That way you don't have to postpone or come out of the retirement for the next several years.
I think this sort of makes me weird, but I love Coverdale in Purple, I love the early Whitesnake (though some of it is a shade bland) and I love the "hair metal" Whitesnake (though some if it is a shade clichéd). I know David probably sees a lot more continuity than we do, but for me, the Purple album was a sort of curio; great songs, and some translated, but I don't know that it was meant to be intertwined like that.
I thought Forevermore was UNBELIEVABLE. Coverdale's voice is liquid gold on the title track (and the acoustic version is even better). I played it for my 15-year-old and she was like "wow, that guy's voice is like silk."
I'd be up for one more, but whether I like it or not will depend on what aspect of Whitesnake they choose to emphasize.
I too don't quite get the need for the "proclamation of finality" that some of these guys do. I get it with a band like REM that put a nail in and say "we're done". No farewell tour, no "one more album", just a press release. But I don't get the need to forecast the future so firmly.