Lusitania
Donor
This is doable for the white dominions - and even African nations starting with the white elite. But the sheer numbers strength of India, and the proud history, still makes this ASB for India, I think.
Correct it was doable for Canada, the Australia, New Zealand and South Africa in the 19th century. British citizens get same voting rights as back in UK. For India they would need to only give the upper Castes right to vote. But giving colonials the right to vote means London has to take those areas into concern and as been stated before that was not the mindset of the government and those in power in UK.
As for exploitation the people in UK were exploited as much and majority of people had no say in government till early 20th
Century.
So we would of needed a different set of circumstances for the people of UK to grant voting rights to those outside the British isles. Heck we need the British people to have different attitudes to not only their own citizens when they left the UK but also locals.
If a significant amount of voters lived in the colonies then more attention to their development not just resource and riches.