No issue at all for ACTON.
Buses have load capacity determined by using an average weight. Hence gas buses have a lower capacity due to a higher tare weight.
If the 18t rule is adopted, it will see the end of Australia's hybrid chassis like the B7RLE etc as we will be able to import chassis direct from Europe. This is the main reason for the 18t rule, to bring us into line with European standards.
Unfortunately Australia's roads aren't up to the standard required to sustain 18t on 2 axles. Road damage will increase relative to axle loading. Buses are the worst offenders for road damage due to having the highest axle loadings of almost any vehicle on the road and the very stop/start nature of the work they perform.