I disagree with the notion that exporting images along with the data is almost impossible. We have plenty of ODK Cloud customers who have very large datasets and they have no problems.
I agree that you are having problems with your install, but it's likely that the problem is with your infrastructure, and not with Central. Did you try my suggestions? If so, update that topic with your findings so we can get to the root cause.
As you noted, Briefcase will continue working even if the core team is not supporting it. And if in the future you find it's not working the way you'd like or it's not feature complete, you are free to improve it.
External storage for blobs is on our roadmap (see External storage for blobs in ODK Central), but it's a lot of work relative to the demand for that feature. If you (or anyone else) is interested in building or funding this feature, email me at yanokwa@getodk.org.