Asana nailed this. Copy their design. Each Kanban column has it's own scrollbar. So, you can scroll down the column with 1500 cards while still viewing the contents of the columns with only 2 or 3 cards. Very intuitive and easy to use.

I've already fielded my first question about lost cards in SmartSuite because the user couldn't figure out where they were on the page after scrolling down hundreds of cards and then scrolling left. The scroll bars in SmartSuite are TINY and he didn't see them. The fix above would take care of it.

Screen shot attached of what it looks like in Asana.