So it might be possible to successfully graft any maple's roots to an acer palmatum; acer buergerianum, acer rubrum, acer saccrum, etc.
I don't think so: the different species of Acer are divided into sections, and each section into series. Grafting only works between species belonging to the same series, so I would say that it's the same for root-grafting.
Acer palmatum cultivars are usually grafted on plain Acer p. stock from seeds. The idea is not only to keep the characteristics of the scion (the grafted part) but also to give the tree enough strength to survive because
some cultivars are not strong enough on their own roots. Others have no problem surviving on their own roots: quite a few cultivars are now available in garden centers now for a very reasonable price because they're made from cuttings, faster, and cheaper to obtain (A. p. 'Phoenix', 'Katsura', 'Orange Dream', ...)
This being said, nursery people, professional grafters probably base their conclusions on the rate of success thay can get for economic reasons. Maybe a graft which is unlikely to take might sometimes work but if it's to improve the look of a bonsai, I wouldn't take the chace.
Incidently, a member of an association of amateur grafters, a former professional horticulturist, came one day to our club to make a demo and told us that some totally different species, and even genus can be grafted onto another. He gave us the example of lilac that can be grafted on privet, to avoid the many suckers lilac produce.