If you need to go down the Etihad on an afternoon in the middle of the week, the tram service is great. For actually attending a match, it's dogshite. Not all of us are fit enough to walk from and into the City Centre, and indeed City's crowd is more elderly than most. Just because someone can walk doesn't mean they are up to walking the best part of four miles, there and back, often in the dark and pissing rain. We are not all 22 any more.
There needs to be a major improvement to public transport before the ground is extended. Personally, I favour an actual railway station on the line near the ground and a proper train service. City can perhaps pay for the station. OK, it will be millions, but so what?