I see very few opportunities for genuine weight reduction whilst retaining both the torsional and impact resistance requirements of a frame as well as other bike components. There is limited opportunity to reduce motor weight and the only real opportunity for weight loss for an EMTB is with advancing battery technology. Obviously the lower powered bikes have their following but from my perspective their supposed light weight is marginal and mostly at the expense of decent wheels and tyres and frame rigidity/impact resistance and/or battery range.
Perhaps everyone is in fact chasing the wrong end of the stick. With the best that can be achieved in terms of weight for a full powered EMTB being about 21kg would it not be more sensible for the manufacturers to be lobbying for an increase in nominal power in excess of the current 250 w together with a marginal increase in max assisted speed? Every vehicle at the end of the day has a power to weight ratio that befits its function. The clarion call for a little increase in max assisted speed.........most especially in Europe and the UK, needs to be taken up by the brands. A marginal increase in nominal power would likely lead to greater reliability of the motors and an increase in assisted speed would reduce the temptation to derestrict...probably again leading to better motor/electrical reliability.
The majority of EMTB components like brakes and tyres are easilly able to cope with a little more motor power so there are no real technical reasons to prevent such a move.