Indeed, the archaic wiring system used for HVAC is a problem. Adapting an ancient hard wired 5-conductor system at the far end of the cable seems backwards.

The furnace itself should have the Ethernet or WiFi connectivity. The thermostat and/or room sensors (temperature, occupancy, whatever) should in no way be restricted by where the original in-wall thermostat wiring happened to terminate. I suggest it be abandoned as if it was an old knob and tube wire.

The classic 5-wire HVAC system carries no smarts at all. No remote diagnostics, no protocols for relaying service or maintenance information. The primary method the furnace has for signaling a problem is partial or complete shut down. When the occupant notices the house getting cold, that is the only signal the furnace could send.*

When confronting the unhappy heating equipment in person, often the only user interface is a single blinking LED. Which can only be seen by peering into a sight hole, and for which the code pattern is erased as soon as the main access panel is removed!

Quite ridiculous, really. In North America the bulk of home HVAC equipment is manufactured by a handful of consolidated companies. It is possible for a far more modern and intelligent HAVC control method to be be defined, implemented, and sold.

* I just diagnosed and repaired a neighbor's natural gas furnace last week. It would sometimes delay or completely refuse the thermostat's demand for heat. Turned out to be a cracked transition assembly which was affecting an air pressure sensor. The furnace would sometimes be able to start, sometimes not. If it could not start four times in a row it would shut down for three hours, then try again.

When the furnace access panel was removed it affected the ambient pressure just enough to allow it to start more often, making accurate fault diagnosis difficult.

The thermostat was replaced as the initial diagnosis suggested it may be a factor. Installed a Honeywell color LCD thermostat with WiFi connectivity . Of course this fancy thermostat still had no idea what was going on with the furnace since it was hamstrung by the antiquated control wiring system.

That furnace was manufactured in 2010. I certainly hope the next furnace will have nothing to do with that dumb five wire system.