There are some (arbitrary) hardcoded limits in badger for value sizes (2GB). These are in place for technical reasons to aid recovery when the data directory in case the data directory becomes corrupted for some reason.
Data would also have to be sent from dgraph to clients and other dgraph instances, so that’s also something that you would want to take into consideration when storing values that large.
Binary blobs aren’t supported right now (although I think it’s a good idea to in the future). As a work around though, you could always do something like Base 64 encoding in a string.