The shaft can be made from 6011 aluminum. The only problem I see is making sure the shaft is centered and balanced, those grinders kick out some speed and torque, so it needs to be balanced.
But a quicker and cheaper method is the 1/4 drill that Shawn posted and the sanding discs from the supplier off of Sawmill Creek. They are even Velcro backed for Frog Morton. And have been tested by 100's of woodturners. I use mine in my Foredom hand piece.
An interesting attachment for an angle grinder. But it seems to me that an angle grinder, unless it has variable speed, turns far too fast for the kind of detail work that most of us do most of the time. Plus it seems very expensive for what you get.
Not excited about sander attachment or 1" diameter sanding disc.
Think angle drill and backup & interface pads and larger size disc a better op. Did not pay $30 bucks for my electric angle drill or my air sander at Harbor Freight.
Even though had trouble with some back-up pads bought here, interface pads and disk are great. I am at fault for destroying a few up pads, also got a few bad ones. I like Vinces blue disc and going to buy some 2" Velcro for my homemade back-up pads a 6-pack only $5. Would like to pick up some 3" blue disc, because think faster than 2 3/8" for some applications.
I use a older hand drill with a flex shaft and sanding pads and discs from www.VincesWoodNWonders.com.I purchased the flex shaft from garet wade tools.
I can get into bowls and does great on the outside.