Can I install/convert a Giant Quick-e+ 2019 to use an Alfine 11 speed IGH? I have a Giant Quick-e+ 2019 and would like to install either a Alfine 11 speed di2 IGH. My first question is, is it compatible? I've been looking at the measurements and it seems all ok. But when I ask different bike shops I get different responses from ones like "why do you want to do that?" to it will break because it's an e-bike. One shop had a look and said it looks like it would work and thought that a bike like that being a commuter type bike would have been a good match, which I agreed and why I want it.

From the whole e-bike breaking the hub thing, Shimano list a version the SG-S7051-11 being revised with "Improved internal structure for better gear engagement" and "Improved performance for both E-BIKE and non-E-BIKE usage" 
So I think for a 250w - 500w e-bike it should be ok, especially for my type of riding which is all on road/pavement and almost all flat?

What do people think about this project? Is it suitable? Will I have issues? What other components do I need? One bike shop said I might need a torque arm for it. I didn't know about this as I thought all I need was the correct washers for a vertical drop out.

Any tips or suggestions would be appreciated. 

Thanks

edit: I would be running the hub with either a 42T or 44T chainring and a 18T sprocket. Not sure if those ratios would be ok?
Seems like a perfectly reasonable project, but there is possibly a technical implementation issue.

The SG-S7051-11 hub is part of Shimano e-bike series that includes a motor, and as you pointed out Shimano says the hub is designed for an e-bike, so it obviously is fine to use it on your Giant.

The dropout spacing offered 135mm only, I would expect the Giant to have that spacing as it has a disc brake. You will need to run a chain tensioner obviously, but that's no big deal.

The difficulty I see is the compatibility of the anti-turn washers with your dropouts. The installation manual here shows quite deep vertical dropouts which the Giant does not look like it has. I believe that is why you were told you need a torque arm. Finding one compatible with the Alfine hub may be a problem, as I believe Shimano does not make such a thing for that hub.