Future's Market is not very good.
There are 2 massive problems with this Rune.
1.) So each time you dip into negative, it charges you 50 gold after you leave the fountain. I don't feel like many players realize this simple fact.
This means that anytime you'd want to use the extra gold to snag a potion or ward, your basically paying double price. Granted, taking an extra potion into a lane could potentially be huge, but the price is just too steep. You essentially delay your late game even more, which is the very thing Future's Market is supposed to work against. It undermines itself in the worst possible way.
2.) At endgame, your limit is generally around 250 to 300 gold. This is pretty low-impact. It's unlikely that it will make a large difference in what you are capable of purchasing. The scaling is really 'meh'.
I'd like to see the rune scale harder, but keep the penalty, so you can pick it and bank on a late-game power spike. Also would have strong impact if you have a horrible laning phase.
Alternatively, would likee to see the 50 gold charge cut in half or dropped entirely. Though this could make the rune pretty nuts.
As it stands, the rune just isn't competitive. What's the point of taking it?
or up is a waste of money.