> here isn't any heat pump out there that will produce water hot enough (e.g. 185F)

For 185:

https://www.arcticheatpumps.com/high-temperature-heat-pump.h...

Or much more common, if you can deal with 176F, the SANCO2 ones will generate that down to -20F.

The hydronic temperatures you're talking about are only required if you have to stick with the existing radiators. They make radiators with little fans that work at lower temperatures, or larger panel radiators. There's lots of options for lower temperature forced hot water.