I was reading a bit between the lines, original was about migrating in, another was saying about a proper synchronization service or dump. In the case of migrating from something outside of Cloud SQL into Cloud SQL you could basically do this today. A dump wouldn't be recommended in my opinion (having done a lot of migrations across cloud providers including several multi-TB databases).
In that case as long as the source has some form of decoding (test decoding plugin or pgoutput) it should work.
That a dump is always the best process anything isn't really true these days (I know someone will show up with a case of why dump is 100% for what they need in moving data around). But, the combination of logical decoding, and pg_upgrade cover most cases.
Admit I was jumping a bit with upgrades, but that is where dump/restore does most often come up, not with migrations.
In that case as long as the source has some form of decoding (test decoding plugin or pgoutput) it should work.
That a dump is always the best process anything isn't really true these days (I know someone will show up with a case of why dump is 100% for what they need in moving data around). But, the combination of logical decoding, and pg_upgrade cover most cases.
Admit I was jumping a bit with upgrades, but that is where dump/restore does most often come up, not with migrations.