Yes, there are some, that's why borg2 will be quite different. But these are no easy or small changes.
Also, borg2 will be a breaking release (offering borg transfer to copy existing archives from borg 1.x repos). It takes long because we try to put all breaking changes into borg2, so you won't have to transfer again too soon after borg2 release.
I don't know about any show-stoppers in borg 1.x.
Design limitations?
Yes, there are some, that's why borg2 will be quite different. But these are no easy or small changes.
Also, borg2 will be a breaking release (offering borg transfer to copy existing archives from borg 1.x repos). It takes long because we try to put all breaking changes into borg2, so you won't have to transfer again too soon after borg2 release.