I've just removed the ekit that i fitted to a bike 6 yrs ago. But as it was a kit, the bike was able to be turned back into a normal bike easily.
I removed it mainly because the battery wasn't getting good range anymore, but i consider 6 yrs not a bad life for the batt, considering how much use it had given and tbf it still had life left in it. It was also only a 9pmp/hr, the smaller the batt the more charge cycles it will get over time. The 8fun hub motor was still working as good as when it was new, but it was always pretty underpowered at only 35nm, so that was another consideration in removing the whole system. Never had any mechanical or electrical faults in the six years. The only real wear i noticed was on the rims of the font wheel the hub motor was laced into, obviously wear from brakes. But it was never a good quality wheel that the motor came laced with.
My current ebike, a ready built Raleigh Pioneer E, is two years old and everything still works as good as the day i bought it. 11amp/hr batt and TranzX front hub motor. Obviously yet to see how long this lasts, but i've no reason so far not to expect many years of service from this bike and the motor has decent torque, so i would be happy to buy a new batt for this bike when the time comes. Again front rim wear from the brakes could be an issue in the future. I think disc brakes are the way to go for ebikes.
Just ordered a Boardman HYB 8.9 E, a much higher quality bike this time, but yet to see how this German Fazua crank drive E system pans out for reliability and durability.
I still think ebikes are overpriced for what they are. As a rule of thumb, i always imagine what the bike would cost as an unassisted bike and add 400 to 500 £ for a hub drive system and 600 to 700 £ for a crank drive system. From this i try to ascertain if an ebike is worth buying for me. Using this equation, it usually means an ebike has to be discounted for me to consider buying it.
For value for money, you cant beat fitting an ekit to a bike of your choice. Its easy to change parts of the e system and the ebike can easily be changed back into a normal unassisted bike. But an ekit rarely looks as good, or is as integrated as a ready built complete ebike.
From being into ebikes myself and knowing people with ebikes that have lasted around 10 years, i've come to the conclusion that ebikes are generally pretty reliable if you steer clear of the cheap & nasty stuff, with only battery replacement as the main ongoing cost of a significant amount.