I think 10 may be a small estimate. You must consider how each coin can fill a specific niche. If you're building a social media platform, for example, you may look for different features than a bank trying to exchange currencies (XRP has advantages there). Bitshares is already breaking new ground in decentralized, low fee commodities trading, but a hospital trying to organize payment records may be looking more for something like a child chain (I believe Ardor is geared toward these purposes), which will undoubtedly have some well developed, targeted "plug and play" options in the future.
The catch is that you're unlikely to directly interact with these coins in the future on a regular basis. You will likely only see your costs reflected in whichever you commonly spend (of which there's room for at least a few just because people like to be different). You may go through a day using 20 different coins (or having 20 used on your behalf) and have absolutely no idea.
tl;dr -- room for 100s of coins, but when you go to the store you'll only see a couple accepted as common currency.