Plenty of cities that will be keen on hosting into the future as it seems to have gone really well in Scotland.
As has been mentioned earlier, I can see the likelihood of two safe games in a row being held before a punt is taken on a risky host. Until 2050 it could go along the lines of:
2022: Durban, South Africa
2026: Cardiff, Wales
2030: Hamilton, Canada
2034: Singapore, Singapore
2038: Christchurch, New Zealand
2042: Adelaide, Australia
2046: Cape Town, South Africa
2050: Edmonton, Canada
Four venues that would host for the first time, four getting it for a second time. I'd imagine that the Comm games are safe for awhile yet. Also think of some other places like Port of Spain in Trinidad & Tobago, Belfast Northern Ireland, Mumbai India. Reckon they could all pull off hosting the event if they wished. Even Nairobi in Kenya, although safety would be something that would be a consideration there.