I have Louise Porter's book on young gifted children but I haven't finished reading it yet, I think education wasthe next chapter so I will let you know if I find anything thast might be useful.
I do wonder wether anything useful would be done in the research because of the huje variations both in 'gifted children' and in 'play-based learning'(Some use playbased learning to be not introducing any academic content at all, while others consider even Montessori to be 'play-based' - its very variable).