Please note that @IronHaiden 's image of a unit entry is for 20mm bases for Hobgoblins in T9A, not AoS, but as @Skink pointed out it might still work. I have no idea if size inflation will be too much, but I hope the new Hobgrots will work well enough alongside older Hobgobs, or at least look good enough in a 4th ed CD army if new Hobgoblins are ranked up in a unit of their own. 
If I’m going to hazard a pure guess, then I think the feet should work on 20mm bases if they are positioned diagonally, like the Sneaky Gits in your comparison picture above. The new Hobgoblins’ feet are not extended all the way to the edges of the round bases, but I’m also not well acquainted with AoS models in general.
Oh, and if the height turns out to be a tad much, then it might be solved rather easily by cutting them at chest height, remove a chunk of the chest (since the gut is the prominent part on old Hobgobs) and reglue the torso halves. It looks like it could be an easy fix with clippers and a hobby knife if cloth is going to be sculpted over the torso anyway, thus hiding the cut.
I’m really curious to see how people will paint these new minis, and not least convert them. It’s so nice to see what looks like a new entry to CDs through the ages being rolled out.
Cheers!