To answer your question of What would also happen if the block size were increased to 1 GB tomorrow is the introduction of new attack vectors, which if exploited would require intervention to resolve by miners, and development.
Like what? What "new" attack vectors? It is already quite cheap to attack the current 1 MB blocksize. What would it cost to attack a 1 GB blocksize vs the current 1 MB blocksize?
The cost is not that significant. Heck, the whole BTC market cap is not that significant.
If there were 6 GB block size bloat per hour?
A financial attack could do this independently.
Miners could do this free-ish.
Small miners would fail, as would all hobby miners.
Full nodes would become centralized, increased 51% risks, etc.
These are just the obvious. No more decentralisation for Bitcoin.