The Switch is region free, and in a disturbingly increasing trend, the only retail versions of some games are from Japan.  I am Setsuna and Bayonetta 1 are only retail in Japan, but have full English versions!  But there is as yet no entries for these games.  Sadly, this will likely only become more common in the future, so I think it is an important thing to add!  Also, you don't even have to do prices, at least initially.  Just give us the option to add them to our collection.  I've noticed quite a few things that have no price but still let you add them.  Thanks!

Since shipping costs are determined by the seller, I feel that there are a lot of times where there are items are seemingly sold at a lower price but once you factor in shipping, the total cost is more in line with the market. I believe shipping is something most people consider when buying a game and therefore, it would be great if it could be included as a column in the historical list prices.

Is a price list coming

The game Pokémon Rumble U had some NFC figurines like Skylanders and amiibos, which were actually created before amiibos, yet are not listed on this site. I would love it if they were on the site. Would make it way easier to buy/sell some to others!

It'd be nice to be able to see what's increasing/decreasing in value as a sort option in my personal collection.

I dont like receiving notifications for every game on my wanted list because most notifications are for over priced games. I have an extensive collection and I'm looking for very specific titles at a discount from ebay or the marketplace. Currently I get 60+ emails a day and 99% of them are overpriced games. Currently I find myself ignoring all notifications and I'm about to turn them off because they are not useful in their current state unless I'm willing to pay any price for a game. This will also alleviate the need to keep the game sniper page open 24/7 for blind deals that are irrelevant for what a collector needs.

Plug & Plays, such as the Jakks Pacific line of licensed "TV Games", and the Radica Plug & Plays. 

Similar to how the stock market works, you can pull up a game and see what its daily Gain/Loss is, see https://www.investing.com/equities/top-stock-gainers

other features like ATH (All Time High) ATL(All Time Low) would be cool too.

The cost basis is recorded for each item.  Keep track of the total cost basis like you do for the total value and total game count.  Keep this value private though like other cost basis info.