I think the alcohol is safe. Flour, though, will definitely degrade over time. In some climates it would also attract bugs. I would think it is fine if the quilt is quilted, bound and a shed within a reasonable period of time -- say, less than 6 months.
i remember making the flour glue too. It was quite wet and very sticky; dried hard. In a quilt you would definitely want a thin layer, not globs.