Just on the manpower thing, I would be curious as to the effect, ramp up and potential of colonial troups in the UK and France.
There definitely was a lot of propaganda about "100 million people in the Empire to defend France!", including in the factories. It does not help with material but we could see a deeper recruitment in the colonies, for combatants and non-combatants, if promises of citizenship or better status are made, which would have extremely interesting butterflies
How many officers did they have who knew native languages? Or natives who spoke French?
They might get some recruits but I'd expect the numbers to be modest.
The real fun would be if Britain tried to extend conscription to Ireland!!