Re: what kind of workloads use/used TSX?
In theory, a lot of things could possibly have used it. Many things that use multiple cores for parallelism, anything that vaguely resembles a database. Don't think "TSX competes with SQL begin/commit/rollback". Instead think "TSX competes with LOCK CMPXCHG & friends for in-memory data structures".
For actual applications, I can't find much online. Apparently a PS3 emulator called RPCS3 used it, Oracle DB, SAP HANA, some HPC workloads.
You could also use it to make a faster version of mincore(), but that function is kind of useless anyway. ;)
It feels like a shame because limited hardware transactional memory was one of the more interesting recent-ish developments in CPUs.