Both Russians and Austrians (and especially Hungarians) are severely lacking in 1/72. Ottomans would be an interesting and exotic option too.
For smaller European armies, I would suggest Danes and maybe a generic set with shako, closed lapels, crossbelts with Sabre and short gaiters for use as late-period Saxons, Westphalians, Swiss, etc.
Also, while we're at it, how about some Seven Years War Russians and French, and maybe some more GNW Russians and Swedes in Strelets's new, much improved sculpting style.
Any of the above would be welcome, particularly the 18th century ones and the Napoleonic Russians and Austrians.
Also, I would agree with those who have suggested that future sets should include more than one command sprue. Most of the units I create require multiple officers, musicians and NCOs, and these write be difficult to obtain elsewhere for some of the suggested armies.