I've never personally drop shipped, but completely agree with Alice's points, and she would know ell as she does have that experience.
The thing is whether drop shipping or not, the points Alice actually made there are quite valid for any business model, especially when it comes to an online platform such as eBay.
Customers to not enjoy waiting for products, in fact my own personal research has shown that the quicker I ship a product, the more I can actually get away with in shipping charges.
Price, as Alice said, if you aren't able to compete on price, then you need to find a new ball game somewhere to join, or you would just be wasting your time.
As I said, key points such as these are important no matter if you are direct selling or agency selling (Drop Shipping), and are something that all sellers need to be on top of.
Stock volume isn't the key, stock that is selling is the key. You could load your store with 1000 items, but if you only have 10 that are selling, then you have 990 products wasting your time. Of course if you have one or two of plenty of those items selling, then that's a different story altogether.
Geographic location, it's the big one that would hurt most Drop Shippers. When you're a customer in the US, an item in Iceland may well not be that appealing, especially when you can find it locally. This essentially ties in with quick shipping, the customer will want the item as quickly as possible on most occasions.
To get around that, your pricing model would need to be super sharp in order to convince them that the extra waiting time for delivery is well worth the saving they are making o the purchase.
I don't consider reputation (feedback) to be as important as it once was on eBay to be honest, but that being said, would you prefer to deal with someone who has solid feedback of 99-100%, or someone who has somewhat suspect feedback of 88-89%?
Now in regards to neutral branding, I'm assuming you are meaning non-branded items?
If so, there is a market for non-branded items for sure, just as there is a market for branded items. My opinion would be that branded items are would be a larger market, but much harder to compete in as it will be far more competitive.
Most niche markets are non-branded markets, not all of them by far, but I would be confident in saying most : )