Well, first of all, I’d love to have had a stash of the “Union Jack” roundels, for the British Raj (i.e. UK’s eastern economy).
For my own use (and my own house rules), I’d also find it useful to have certain two-sided roundels:UK, with Canada on reverse Union Jack, with ANZAC on reverse
On a related note, even though they aren’t round (and hence not “roundels”), I’d have liked for the factory markers to also be two-sided, with the minor factory symbol on one side, and the major factory symbol on the reverse.
Having a reverse side on the air base markers – to indicate which air bases have scrambled this turn – would have been useful.
I hope these ideas prove useful to you. I look forward to hearing what options you can provide for these ideas of mine.