So basically we would have a shop for DEC, one for vouchers, one for glint? How does that make sense? Glint would basically be untouched by this solution so we can disregard the glint shop, but DEC and vouchers would just have their own exclusive shop while still being tradeable?

All you do is force people to exchange between the two tokens if they want to make a purchase. If there is something you want in the "DEC shop" you sell vouchers (if you have any) and the other way around. Forcing trade of 2 tokens on a secondary market sounds very new user unfriendly to me.

Apart from that you have to artificially come up with what new voucher only items? At least you can't use items from the glint shop, otherwise you break the idea of glint. And putting items from the DEC shop there and you might as well just give out DEC instead of vouchers.

I think the idea is interesting at first glance, but after a while you realize that the only one benefitting would be the VOUCHER:DEC trade.