White lead is Lead (IV) oxide, the famous white pigment in paint, (ie lead paint). titania (TiO2) is what has replaced white lead in almost all paints, completely non-toxic, it is even used as a pigment in foods and cosmetics.
One of the few areas where titania has not replaced white lead has been in the shipping industry, lead paint is still better at ressisting corrosion.
You can use Titanium dioxide to replace the white lead in your recipe. There is a company that sells a commercial form of guesso called liquitex, that uses titanium dioxide.
Liquitex makes a respected line of acrylic artist's paints, including a "gesso". But while their product can be used for preparing surfaces for acrylic or oil painting, it's not really useful for gilding mainly because it has no quality of hardness. It doesn't respond to burnishing except by breaking up.
Titanium dioxide was one of the first things tried as a substitute for the white lead, probably for the same reason you suggest it. But while it's now the standard replacement for white lead as a pigment in paint and works pretty well (not quite as opaque or "buttery"), pigmentation must have been only a secondary role for the white lead in gesso because people have been fiddling with different proportions of titanium dioxide for years now without noticable success. I had high hopes for it years ago myself, but I honestly can't detect much real difference in the receipe whether I put it in or leave it out.
I have no training in chemistry at all, so my ideas might seem naive. I thought that paint tubes were still made of lead foil but discovered that they're apparently made of aluminum these days. So that's when I started to wonder what exactly the white lead was contributing to the gesso and whether aluminum might not, at pigment-level granularity, substitute for it.
My original thought was to use aluminum oxide, since it too is white, but then I discovered it's a high-class abrasive so I thought that might not be such a nifty quality to impart to the gesso. So I was back to thinking about plain aluminum powder.
I do a little work with metals, mostly silver and copper, in connection with jewellery and enameling, so I'm used to thinking of metal as being fairly plastic - I use a steel burnisher to remove scratches, for example, and harden or soften a piece with hammer or fire. So it seems natural to imagine soft, powdered aluminum "loosening" the gypsum crystals enough to plasticise the gesso compound. But aluminum powder is expensive and (apparently) dangerous, and gesso takes a month to make, so I thought I'd get some advice from real chemists before I leaped in and maybe wasted time and money.