That is also quite nice, my main problem with this approach is - can we by now assume that the mkgmap:country tag is 99.9% available correctly when using precompiled bounds?
I wouldn't take that for granted - I use my own Europe extract of Poland and border areas of neighbour contries, I generate precompiled boundaries but often a lot of places outside Poland get mkgmap:country assigned as 'POL' because I use --country-abbr=POL and level 2 administrative boundaries are so incomplete (as extract do not cover whole countries, only their parts) that mkgmap can't process them.