Phyto - I have been building muscle just fine with minimal protein supplementation (a scoop of pea protein/some grains), definitely nowhere near the 1g per lb body weight rule. In fact I've never lived up to that rule even when I was a meat eater. I believe I'll keep on just fine with natural protein intake without supplementation. I think the key to maintaining/building muscle mass is making sure your body has enough calories so there are no cannibalizing hormones going rampant. This is VERY easy to do with fruits.
I agree with you that most people put way too much emphasis on protein. I do not supplement protein either, but still average 1g protein per kg of body weight(which i assume you meant kg instead of pounds) and I have also been able to maintain/increase muscle mass. But I eat a lot of beans/nuts/seeds besides vegetables/fruits.
Generally fruit are the lowest in protein content. Do you have any idea how much protein you have been taking in on an average day and how much you will be when you switch to mainly only fruit intake?
It would be interesting to know your protein intake and see how your muscle mass maintains/increases during the summer fruit months.
This isn't intended to be a smartass comment or to demean you in any way. I am truly interested in seeing how this goes for you. Good luck.