It depends.
The odds against an eBook store:
0. Undefensible business model - little/no barrier to entry, few patents, anyone can start such a store
1. Getting advertising and distribution at scale
On the plus side:
2. It might work at a tiny scale for niche categories/communities/local businesses.
Otherwise, I wouldn't waste too much time on it. I would something that's more difficult to copy or emulate.