I'd already be happy if I could pin a second destination in the "Backup to another location" option as it is now, and I believe it would be really easy to implement.
If you're thinking about adding value to your product, I think multiple destinations for a single job definitely could be useful for local + offsite backups. I wouldn't want to maintain complex file-based selections (with alot of include/exclude) duplicated in two separate jobs. I could even see people wanting a separate schedule for each destination (e.g. everyday to local destination and once a week to offsite destination, using the same selection). I got multiple selections and multiple destinations (per selection) covered with CrashPlan right now, in parallel with VEB backing up locally to a NAS. CrashPlan is doing a great job at keeping alot of retention while keeping backup files smalls, and low network traffic for offsite backups, but it's not designed at all for baremetal recovery (and it require software running on remote destination, which is not always possible). Both software have different strengths and are a great complement to each other.
I can also see easily why multiple jobs are a popular demand:
1. file-based backup everyday, critical files only, keeps the backup chain smaller with more retention, use 2nd destination as offsite backup.
2. disk-based system partition only, on a less frequent schedule (e.g. once a week), for baremetal revovery. could use ad-hoc on alternate destination from time to time.
3. full system backup triggered manually once in a while for some reason.
For now, I use an alternate (third) backup software when I need a temporary backup of system partition only (or a full system backup) because I don't want to mess with my everyday backup job/chain. Current ad-hoc backup function could be used in my situation for baremetal recovery of system partition only, but the job also includes files on other partitions so it takes longer and waste more disk space.