Ah that old chestnut - going for the easiest/safest conviction. Usual battle of the Lawyers stuff.
The discussion originally started with the poster stating 'severe injuries'. He then went on to mention if a person died. You suggested (for both) that it would all be relatively rosy and sorted out for the offending rider by throwing an ABH charge at it and whacking it into a Magistrates.
If you're happy going for an ABH charge when someone is left in a wheelchair for the rest of their life then you (as a prosecutor) would be selling yourself short IMO, and certainly that of the victim.
And I maintain (contrary to your comments) that a death involving a derestricted ebike will get far more involved than a Sec47 ABH in a magistrates. For sure, I certainly wouldn't want to be the rider gripping the rail in those proceedings.
BTW, I don't think a jury would have too much trouble finding that a rider is 'reckless' by default if they are using a derestricted ebike in a public place with people around. And I still don't understand your focus on the 'aggravating factor' or that it becomes 'complex' - it matters not the ins and outs of how the bike has been modified etc - the fact remains it will be classed as an unlicensed, untaxed, unregistered and uninsured motorcycle, and would be treated as such in terms of traffic law.
Interesting to hear your take on it though. You have ridden a fair few derestricted bikes haven't you?
In answer to your last point, yes. I have ridden ebikes which are capable of exceeding 15.5mph. Technically I've never de-restricted an ebike (to tamper with a motor which the manufacturer did not want for the product). The ebikes which I have built (some of them anyway), are capable of exceeding 15.5mph. And thus, I have not (nore ever) will take a motor and add third-party software or hardware to tamper with the settings.
Hell, I've never touched the BLevo app whereas most riders with specialized ebikes have 
.
As for the circumstances if death is caused (or serious life changing injuries) as a result of the assault, that is a different circumstance which would push the criteria into a different offence category. It 'may' fall under 'death by dangerous/careless driving' as the points to prove for this offence are,
-being driver of a mechanically propelled vehicle dangerously
-caused the death of another person
-on a road or public place
s1 of the Road traffic Act 1988
Or,
Wanton & Furious Driving which the points to prove are,
-in charge of a vehicle or carriage,
-by wanton/furious driving/racing or other willful misconduct,
-did cause bodily harm to be done to another
s35 of the offence against the Person Act 1863.
Either offence is indictable but I illustrate my point. As a case would need to prove 'beyond reasonable doubt' that an offence has been committed.
The definition of a vehicle is a conveyance (usually with wheels), built to (or can demonstrate) transporting of people, goods etc. Examples of such vehicles would include, car, cart, sledge, truck, carriages etc. Essentially, anything which is a receptacle in which something is placed in order to be moved.
So in other (again, my mind as if I was a prosecutor), I would persue the offence which leaves no room for failure.