I think that'd be useful for people who want to split their vends among the various machines or for those who want to keep track of how many times they have vended that day. I know we can track it by taking note of our tokens on hand but I always forget to do so. ^_^"
You can also track it by noting your inventory items, so I don't know how necessary this really is tbh. But it doesn't really make a difference to me if it's implemented or not.
Well, I for one, vend my ~250, sort out expensive-ish items (LOLOL you know, those 2 items) or items I need, and then frag the rest. Rinse, repeat. I'd like to know as I'm doing it so I don't have to check my inventory to make sure I don't go past the 250 mark (well not even, more like 246 because locked item) because it won't show all the items and I don't wanna frag something I might have needed.
So yea, if this is easy enough to code, why not?
I don't think this is a bad idea though I'm not sure if it's worthwhile as they do notify you when you've reached your max by telling you that you can't vend any further for the day.
I think this is a good idea. They already keep track of how many items you vend, so why not display it right under where your number of wizard tokens display under the vending machine?

It would definitely be nice if they showed it, however while I do the same as does, I simply look at how many tokens I have when I start, do that -500 and stop when I hit that number. That's 250 perfectly. Problem solved.
It'd be nice, but I don't know if it's that needed.