I'd say most of the trams currently being ordered around the world are 30
metres. It's pretty-much the modern standard tram. Much depends on the
interplay of various factors, including infrastructure, space, ability to
extend platforms, headways, line capacity. Melbourne is fairly unique
having not many platforms. I can't think of many cities nowadays without
platforms (Toronto?).

Chronic and ongoing under-investment is the state of play with Melbourne's
tram system. Prometheus bound.

Tony P