NZ doesn't seem to be in hurry to cap ebike speeds which is good thing. I own a 32kmhr and 50kmhr(dongled 25kmhr )ebikes. My cruise speed on 32kmhr is 28kmhr as next gear is little tall for 30kmhr, after 30kmhr assist drops off, find this speed fine for 10-15km commutes. On dongle bike it's 35-40kmhr which is nice pace, with odd higher burst to 50kmhr when needing to mix it with cars. Really needs a x3 dongle as 50-55kmhr is ideal for taking lane with cars. The 45kmhr is stupid speed, to slow to share road with cars and to fast for cycleways, the idiots in Europe that came up with that speed have never ridden a bike on road, car drivers also find it frustrating as bike is to fast to pass quickly.
The 25kmhr speed made sense when odd ebike was sharing crowded dutch cycle lanes with bikes cruising at 15-20kmhr. That is now no longer case as ebikes are heading to 50% or more of commuter bikes in europe. In countries like Australia and UK they should've gone for 32kmhr as few normal bikes on cycleways are typically doing 20-35kmhr.
When it comes to MTBing I've never found 25kmhr cutoff to be much of issue, on uphill single tracks rarely hit cutoff. Only on flat forestry roads is higher speed useful. Most MTB park tracks are one way so collisions shouldn't be issue, between fast eMTBs and MTBs.