Fun fact: TimescaleDB exists because we were using InfluxDB + Postgres for a previous IoT project and also found it unworkable (developer experience, query language, reliability, scalability and performance, operations, etc).
We first built TimescaleDB as "Postgres for time-series" for our own needs and then decided to open-source it for others. :-)
Timescale engineer here. I'm betting we'll see a nice win; we tend to see write-mostly workloads the UNDO shouldn't be too expensive, and the smaller tuple sizes should be nice. We've built Timescale to be compatible with custom storage engines, so it should work as a drop-in, though of course until we've tested it we won't be sure.
Another Timescale engineer here. As previously pointed out, zheap should work as a drop-in in TimescaleDB. In fact, I just tried it and it works. However, it currently requires an unmerged PR to work properly: https://github.com/timescale/timescaledb/pull/2082, as well as further testing.
We first built TimescaleDB as "Postgres for time-series" for our own needs and then decided to open-source it for others. :-)